Article

Citation: Obeid, R.; Andrès, E.; Ceška,ˇ R.; Hooshmand, B.; Guéant-Rodriguez, R.-M.; Prada, G.I.; Sławek, J.; Traykov, L.; Ta Van, B.; Várkonyi, T.; et al. Diagnosis, Treatment and Long-Term Management of Vitamin B12 Deficiency in Adults: A Delphi Expert Consensus. J. Clin. Med. 2024, 13, 2176. https://doi.org/10.3390/jcm13082176

Academic Editor: Carlo Finelli

Copyright: © 2024 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

1. 1 Department of Clinical Chemistry and Laboratory Medicine, Saarland University Hospital, 66421 Homburg, Germany
2. 2 Department of Internal Medicine, Diabetes and Metabolic Diseases, Hôpitaux Universitaires de Strasbourg, 67091 Strasbourg, France
3. 3 IIIrd Department of Internal Medicine, Center of Preventive Cardiology, University General Hospital, Charles University in Prague, 110 00 Prague, Czech Republic
4. 4 Aging Research Center, Karolinska Institute, 171 65 Stockholm, Sweden
5. 5 Department of Neurology, Benedictus Klinikum Tutzing, 82327 Tutzing, Germany
6. 6 Department of Psychiatry and Psychotherapy, Ludwig Maximillian University Hospital, 80539 Munich, Germany
7. 7 INSERM, UMR_S1256, NGERE–Nutrition, Genetics, and Environmental Risk Exposure, Faculty of Medicine of Nancy, University of Lorraine, 54500 Vandoeuvre-lès-Nancy, France
8. 8 Department of Biochemistry, Molecular Biology, Nutrition, and Metabolism, University Hospital of Nancy, 54000 Vandoeuvre-lès-Nancy, France
9. 9 Clinical Department of the National Institute of Gerontology and Geriatrics “Ana Aslan”, University of Medicine and Pharmacy “Carol Davila”, 011241 Bucharest, Romania
10. 10 Department of Neurology & Stroke, St. Adalbert Hospital, 80-462 Gdan´sk, Poland
11. 11 Department of Neurological-Psychiatric Nursing, Faculty of Health Sciences, Medical University of Gdan´sk, 80-210 Gdan´sk, Poland
12. 12 Department of Neurology, University Hospital “Alexandrovska”, Medical University, 1431 Sofia, Bulgaria
13. 13 Vietnam Institute of Diabetes and Metabolic Disorders, Hanoi Medical University, Hanoi 116001, Vietnam
14. 14 Department of Internal Medicine, University of Szeged, 6720 Szeged, Hungary
15. 15 Consultant in Neurology and Clinical Neurophysiology, 41844 Wegberg, Germany

* Correspondence: [email protected]; Tel.: +49-6841-1630711 † Membership of The Vitamin B12 Consensus Panelists Group is provided in the Acknowledgments.

Abstract: Background/Objectives: Vitamin B12 deficiency can cause variable symptoms, which may be irreversible if not diagnosed and treated in a timely manner. We aimed to develop a widely accepted expert consensus to guide the practice of diagnosing and treating B12 deficiency. Methods: We conducted a scoping review of the literature published in PubMed since January 2003. Data were used to design a two-round Delphi survey to study the level of consensus among 42 experts. Results: The panelists agreed on the need for educational and organizational changes in the current medical practices for diagnosing and treating B12 deficiency. Recognition of clinical symptoms should receive the highest priority in establishing the diagnosis. There is agreement that the serum B12 concentration is useful as a screening marker and methylmalonic acid or homocysteine can support the diagnosis. Patient lifestyle, disease history, and medications can provide clues to the cause of B12 deficiency. Regardless of the cause of the deficiency, initial treatment with parenteral B12 was regarded as the first choice for patients with acute and severe manifestations of B12 deficiency. The use of highdose oral B12 at different frequencies may be considered for long-term treatment. Prophylactic B12 supplementation should be considered for specific high-risk groups. Conclusions: There is a consensus that clinical symptoms need to receive more attention in establishing the diagnosis of B12 deficiency. B12 laboratory markers can support the diagnosis. The severity of clinical symptoms, the causes of B12 deficiency, and the treatment goals govern decisions regarding the route and dose of B12 therapy.

J. Clin. Med. 2024, 13, 2176. https://doi.org/10.3390/jcm13082176 https://www.mdpi.com/journal/jcm

Keywords: diagnosis; neuropathy; cognitive decline; anemia; treatment; vitamin B12 deficiency

Vitamin B12 (cobalamin) deficiency can affect several organs, such as the bone marrow and the peripheral and central nervous systems [1]. The signs and symptoms of deficiency are variable and mostly nonspecific. Patients often seek help in primary medical care.

Dietary sources of vitamin B12 are foods of animal origin such as red meat, liver, fish, and dairy products. Insufficient dietary intake of vitamin B12 (<4–5 µg/day) can cause vitamin B12 deficiency. In addition, intestinal absorption of vitamin B12 requires the release of vitamins from food proteins, normal secretion and function of intrinsic factor, and appropriate gastrointestinal acidity. Malabsorption of vitamin B12 is the main cause of clinically manifested vitamin B12 deficiency among adults. Pernicious anemia (lack of intrinsic factor or antibodies against intrinsic factor), atrophic gastritis, and other gastroenteric diseases can cause B12 malabsorption. People with vitamin B12 deficiency caused by malabsorption disorders show gastrointestinal symptoms (episodes of abdominal distress, distension, nausea, and diarrhea) [2] in addition to symptoms such as neuropathy that is caused by the deficiency itself [3].

Manifestations related to the hematopoietic system such as megaloblastic anemia can be diagnosed using widely available laboratory markers. Approximately 30–50% of patients with vitamin B12 deficiency have some degree of neurological involvement [4]. Psychiatric symptoms such as mental and mood disorders and cognitive dysfunction are also common in people with B12 deficiency [4–6]. If the diagnosis of neuropsychological manifestations of vitamin B12 deficiency is delayed, symptoms may become irreversible [7–9] within variable time intervals (months to years), depending on residual B12 stores in the liver.

The serum concentration of vitamin B12 is a commonly used marker of vitamin B12 status. The majority of vitamin B12 in blood is bound to haptocorrin, which is not available for B12-dependent enzymatic reactions in cells. Holotranscobalamin is vitamin B12-bound to transcobalamin and constitutes a small fraction of total serum B12, which is biologically active. Adenosylcobalamin and methylcobalamin deficiency results in increased plasma concentrations of methylmalonic acid and homocysteine, respectively. Circulating vitamin B12 may not be lowered in all patients with B12 deficiency [10]. Using metabolic markers of B12 status like methylmalonic acid and homocysteine to aid in the diagnosis of clinically manifested vitamin B12 deficiency has advantages, but also shortcomings [10,11], such as the high costs of measurements, the limited availability, and the impact of renal insufficiency on the concentrations.

The severity of vitamin B12 deficiency symptoms at first presentation affects the choice of treatment modality. For example, initial parenteral treatment is used when the clinical symptoms are severe [12]. For the long-term management of pernicious anemia after B12 replenishment, parenteral treatment with B12 every 1–3 months seems sufficient to prevent a relapse [13–15]. More recent studies have suggested that the effectiveness of parenteral and high-dose oral B12 (1 mg/d) is similar in correcting serum concentrations of vitamin B12, though the evidence is of low quality. Nevertheless, high-dose oral B12 can likely be used for maintenance treatment in many patients [13–15].

The UK National Institute for Health and Care Excellence (NICE) released guidelines intended to facilitate the medical care of people with vitamin B12 deficiency specifically in the UK [16]. However, due to uncertainties and lack of evidence on multiple aspects related to the diagnosis and treatment of vitamin B12 deficiency, widely accepted guidelines are still needed due to between-country differences in medical practices, healthcare systems, and generally limited resources. The aim of this study was to establish an internationally acceptable consensus based on a review of the literature published over the past 20 years.

Following a scoping review of the literature, we summarized consistent results related to aspects of the diagnosis and treatment of vitamin B12 deficiency. In areas with insufficient evidence, we used a modified Delphi method to establish a practice-oriented expert consensus that can guide the medical care of people with vitamin B12 deficiency and those at risk for deficiency.

1. 2.1. Methods of the Scoping Review
2. 2.2. Recruitment of Scientific Board Members and Panelists

The scientific board members were invited by the leading authors (RO and KR) based on medical expertise, practical experience in the field of B12 deficiency, publication records, seniority, and willingness to participate. Nine out of twelve experts accepted the invitation to serve as scientific board members. The remaining three experts declined due to conflicts of interest. The scientific board consisted of one pharmacist and nine medical doctors (four from neurology/neuropsychiatry and five from internal medicine). The scientific board was responsible for planning the study, setting and refining the survey questions, and discussing and interpreting the results of the surveys. The board met once prior to the first survey round (June 2023) and once after the second survey round (November 2023). To ensure the neutrality of the results, the scientific board members were not eligible to participate in the surveys.

The panelists (the survey participants) were recruited through different channels. First, all corresponding authors of the 151 original articles identified through the literature search were invited to participate. Second, experts were identified through professional networks of board members, in addition to key opinion leaders in the field who had not published original studies in the last 20 years. Forty-six panelists agreed to participate in the survey. The first survey round was completed by 46 panelists, while the second survey was completed by 42 panelists (4 non-responders in the second round). Two online surveys were conducted using the SurveyMonkey Genius® program. For both surveys, the responses of the panelists were anonymous.

1. 2.3. Conduction of the Delphi Survey
2. 2.4. Data Analysis and Consensus Definition

After returning the answers of the first survey round, we calculated the mean and 80% confidence intervals (CIs) of the percentage of panelists who agreed with each of the answers. The first survey included widely formulated questions that needed to be prioritized for a more focused second survey. Therefore, wider uncertainty intervals (80% CIs) were used in the first survey cycle. Only answers with a level of agreement of at least 50% (as a lower bound of the 80% CI) were revised and used in the second round of the survey. In the second round of the survey, the upper two categories on a five-point Likert scale (the “agree” and “strongly agree” categories) were combined. A question was considered to reach a consensus if the combination of the “agree” and “strongly agree” categories constituted at least 50% of the total responses (50% as the lower bound of the 95% CI of the mean response). Questions that did not achieve consensus were considered topics with uncertainty or candidate topics for future research. The mean percentage and the 80% or 95% CIs of the panelists who agreed with the answers of the survey rounds are shown in Tables S4 and S5, respectively.

1. 3.1. Vitamin B12 Deficiency in the Medical Literature

Several topics showed consistent results between the studies (Table S6). Macrocytic anemia is not related to the presence or absence of neurological symptoms or their severity [11,18–21]. The serum concentration of vitamin B12 is commonly used as a primary marker of vitamin B12 status. However, 30–40% of people with neurological or hematological symptoms related to B12 deficiency may have normal vitamin B12 concentrations [22–25]. Serum vitamin B12 concentrations below 148 pmol/L (or 156 pmol/L in certain studies) are commonly considered to suggest a frank deficiency [26–30]. Serum B12 concentrations between 148 and 220 pmol/L or 260 pmol/L are often considered to indicate mild deficiency [31–33]. Some studies measured plasma homocysteine concentrations [7,34] or both homocysteine and methylmalonic acid [35–37] along with serum B12. For homocysteine and methylmalonic acid concentrations, there is a large variability in the cutoff values and combinations with other markers [11]. Low serum B12 concentrations and elevated methylmalonic acid [38] are not consistently correlated with the presence or severity of polyneuropathy or the clinical response to B12 treatment [39]. Vitamin B12 treatment increases serum B12 concentrations and decreases methylmalonic acid and homocysteine levels [18], but the normalization of these markers does not always correspond to clinical improvement. In general, determining the severity of B12 deficiency and the response to treatment primarily relies on evaluating clinical symptoms.

The use of the glucose-lowering drug metformin is causally related to lowered serum concentrations of vitamin B12 [40–46]. The effect has been shown as early as 3 months after

starting the drug [47]. Low serum vitamin B12 concentrations in people using metformin are associated with hyperhomocysteinemia [48], a higher incidence of neuropathy [49,50], and worse neuropathy scores [51]. A recently published longitudinal study showed that people using metformin had a greater risk of neuropathy [HR = 1.84 (95% CI, 1.62, 2.10)] than those not using metformin [49]. There was a dose-response association between the daily dose of metformin and a greater risk of neuropathy [49], which could suggest that low vitamin B12 concentrations are a direct cause of neuropathy in those patients. Vitamin B12 supplementation can increase serum B12 concentrations in users of metformin [47,52], but it remains unclear whether it may reduce neuropathy risk.

Vitamin B12 deficiency is common in elderly people [53,54] and is often explained by food-cobalamin malabsorption [55,56]. There is currently no clear evidence that vitamin B12 deficiency has an etiological role in frailty [54] or sarcopenia [57] in elderly people. The presence of some gastrointestinal disorders constitutes a major risk factor for vitamin B12 deficiency. Pernicious anemia often occurs parallel to other autoimmune disorders [27] and in people who are first-degree relatives of patients with this condition [58]. Positive antibodies against intrinsic factor or parietal cell antibodies are found in 30–50% of patients with neurological manifestations related to B12 deficiency [3,4]. Pernicious anemia may be associated with a deficiency of multiple nutrients, such as folate and iron [59]. Lowered serum vitamin B12 has been reported in people with atrophic gastritis [2,60], Crohn’s disease [61–63], celiac disease [64], infection with H. pylori [65], gastric surgeries [66–70], and chronic treatment with proton pump inhibitors [71]. Up to 70% of patients who undergo gastrectomy may develop vitamin B12 deficiency 12–24 months after surgery if not supplemented with the vitamin [72,73].

In people with vitamin B12 malabsorption, 1000–1500 µg/day of oral vitamin B12 [74–77] or 1000 µg i.m. B12 every 1–3 months is adequate as a maintenance treatment to keep serum B12 concentrations within the reference range [18,78]. Lowered serum concentrations of vitamin B12 are unlikely to be corrected by using 3–6 µg/day B12 from food supplements or high oral B12 (1000 µg) provided once weekly [30,73,79]. High dose oral and i.m. protocols are likely to be equivalent in correcting serum B12 concentrations [14,15,26]. Available vitamin B12 forms such as cyanocobalamin and methylcobalamin are safe and beneficial [80,81].

Neuropsychiatric conditions are common in patients with B12 deficiency, although the available studies are heterogeneous regarding patient characteristics and the diagnostic tools employed [3–5,29,33,82–87]. This variability in particular concerns the differentiation between peripheral sensory neuropathy and sensory neuronopathy (gangliopathy) alone or as part of the subacute combined spinal cord degeneration (SCD) syndrome. At least 50% of patients have both manifestations concurrently [24]. Therefore, in patients with sensory symptoms, differential diagnoses for both disorders need to be considered.

The time needed for hematological and neurological symptoms to recover after starting vitamin B12 treatment varies among subjects [14,88], but high-quality follow-up studies are not available. In general, subjective improvement occurs earlier and is more impressive than objective recovery of neurological function [29]. The earliest subjective improvements after B12 treatment occurred for paresthesia and balance, leading to full recovery [87]. Up to 25% of patients have been reported to retain severe neurological symptoms despite the normalization of blood marker levels [8,9]. In approximately 20% of patients with neurological signs and symptoms, recovery may become evident after 3 months of starting the therapy and remain partial [3]. Symptoms of neuropathy mostly improve within several months but may take up to one year for sensory symptoms to resolve after the start of B12 therapy [4]. In patients with SCD, sensory neuronopathy may improve after 7 weeks of B12 therapy (range: 2–32 weeks) [24]. In general, B12 treatment for a minimum of 2 months improves signs and symptoms in all patients with SCD, while Romberg’s sign and mild sensory disturbances in the toes and fingers may persist in some patients after several weeks or months of B12 therapy [7,89]. In a group of deficient patients who were treated and followed up for 2–24 months, the patients with stomatitis showed a complete

recovery [4]. In another study, neuropsychological tests were corrected after 6 weeks of multiple i.m. injections of 1000 µg B12 [90]. Functional recovery measured by an activity of daily living score may take as long as 12 months, although single cognitive tests may already show some improvement within 3 months [82].

The duration and severity of pretreatment deficiency symptoms have a clear impact on the time course and degree of recovery after starting B12 therapy [1,86], thus emphasizing the importance of early identification and prevention.

1. 3.2. Results of the Delphi Survey

1. 3.2.1. Characteristics of the Survey Panelists
2. 3.2.2. Delphi Survey Rounds

The questions that received consensus in the first survey (Table S4) were revised and used in the second survey (Table S5). The final consensus statements are summarized in Tables 1 and 2.

, x FOR PEER REVIEW 7 of 19

Figure 1. Symptoms of B12 deficiency ordered from the most to the least difficult for being linked to B12 deficiency. Although neuropsychiatric symptoms are more frequent than hematological abnormalities, they are less specific, more demanding to recognize, and thus more difficult to link to B12 deficiency.

Figure 1. Symptoms of B12 deficiency ordered from the most to the least difficult for being linked to B12 deficiency. Although neuropsychiatric symptoms are more frequent than hematological abnormalities, they are less specific, more demanding to recognize, and thus more difficult to link to B12 deficiency.

Table 1. Expert consensus was reached after 2 survey cycles on all of the following topics related to the diagnosis of vitamin B12 deficiency and its causes.

Questions n (Panelists) 1 Mean (95% CI) 2 Identification of vitamin B12 deficiency: Challenges, barriers and obstacles

1. 1. The delay in diagnosing B12 deficiency in a significant number of patients may be due to the following factors:
2. 2. The following initiatives can reduce the burden of unidentified B12 deficiency:
3. 3. Signs and symptoms of B12 deficiency may affect multiple organ systems at variable frequency. The crude order of affected systems (highest to lowest prevalence) is shown in Figure S3.
4. 4. The most difficult symptoms to link to clinically manifested B12 deficiency are
5. 5. Clinically manifested B12 deficiency is commonly first identified in primary medical care. Some patients may require referral to a specialist. Referral of patients to gastroenterologists is least frequent compared to referral to neurologists/psychiatrists and hematologists
6. 6. Concordance with the diagnostic pathway shown in Figure 2. 42 0.76 (0.61–0.88)
7. 7. Considering the cost-benefit and the added value of advanced laboratory tests beyond plasma B12 concentrations and blood cell count:
8. 8. Because chronic use of metformin in patients with diabetes is associated with lower plasma concentrations of B12 and linked to the frequency and severity of neuropathy, measurement of B12 status once per year in this group of patients can help detecting a deficiency prior to clinical manifestation.

40 0.83 (0.67–0.93)

Table 1. Cont.

Questions n (Panelists) 1 Mean (95% CI) 2

9. If plasma B12 concentrations far above the reference range are encountered in a person without specific medical conditions:

1. • Inquire if the person is using any supplemental B12 source (food
2. • If the person is not using a B12-supplement, repeat plasma B12 test after
3. • Rule out disturbed blood count, liver and renal function markers that may explain high plasma B12 levels due to liver or kidney diseases or undiagnosed malignancies.

39 0.85 (0.69–0.94)

1. 10. A holistic approach is deemed necessary for diagnosing B12 deficiency and identifying the cause(s). This includes:
2. 11. The following conditions may provide clues for B12 deficiency being due to B12 malabsorption:
3. 12. In context of the B12 diagnostic work-up, folate and iron status should also be

42 0.95 (0.84–0.99)

assessed.

1 Total number of the panelists who answered each of the questions. 2 Mean percentage and the 95% confidence intervals of the panelists who considered themselves qualified to answer the question and chose “agree” or “strongly agree” to the answer. We considered that a consensus was reached when the lower bound of the 95% confidence interval was 50% or higher. T1DM, type 1 diabetes mellitus.

3.2.3. Consensus on the Clinical Practice of Diagnosing Vitamin B12 Deficiency

The panelists agreed that the delay in the diagnosis of vitamin B12 deficiency may be explained by barriers such as the variability of symptoms, low doctor awareness of the disease, not paying attention to the patient’s symptoms, and limited access to modern laboratory markers (Table 1). There is agreement that some of these barriers can be overcome by educating both doctors and patients. The panelists agreed that symptoms related to the peripheral and central nervous systems are the most common symptoms in patients with clinically manifested vitamin B12 deficiency (Figure S3). At the same time, it was agreed that symptoms affecting the central nervous system (mental function and neurological function), followed by those affecting the peripheral nervous system, are the most difficult symptoms to link to B12 deficiency (Figure 1), suggesting the need for more

Family history of pernicious anemia.

J. Clin. Med. 2024, 13, 2176 9 of 18

• Chronic gastrointestinal conditions.

specific awareness in a primary medical care setting and an improvement in examination options. Moreover, there is agreement that metabolic biomarkers such as methylmalonic acid and homocysteine can be useful in guiding the diagnosis of vitamin B12 deficiency and optimizing and monitoring treatment with vitamin B12 (Table 1). The panelists agreed that the periodic measurement of serum concentrations of vitamin B12 can be helpful in identifying people at risk of deficiency, such as people receiving long-term metformin treatment.

In context of the B12 diagnostic work-up, folate and iron status

42 0.95 (0.84–0.99)

Total number of the panelists who answered each of the questions. Mean percentage and the 95% confidence intervals of the panelists who considered themselves qualified to answer the question and chose “agree” or “strongly agree” to the answer. We considered that a consensus was reached when the lower bound of the 95% confidence interval was 50% or higher. T1DM, type 1 diabetes mellitus.

Figure 2. Diagnostic algorithm for vitamin B12 deficiency assessment. The vitamin B12 deficiency diagnostic algorithm was based on a consensus of 42 panelists [mean (95% confidence intervals of the agreement level) = 0.76 (0.61 − 0.88)]. * Full blood cell count and serum B12 concentration; § Serum concentrations of holotranscobalamin, methylmalonic acid, total homocysteine, gastrin, antibodies against parietal cells and/or intrinsic factor and specific tests of the respective specialties. Special diagnostic tests are subject to availability.

Figure 2. Diagnostic algorithm for vitamin B12 deficiency assessment. The vitamin B12 deficiency diagnostic algorithm was based on a consensus of 42 panelists [mean (95% confidence intervals of

If concentrations of serum vitamin B12 are above the reference range and people have no specific medical conditions, the panelists agreed that inquiring about the usage of supplemental vitamin B12, repeating the measurements of serum B12 after a given time interval, and measuring routine blood markers of renal or liver function or exploring malignancies [91] could explain the cause of high serum B12 (Table 1).

In the context of clarifying the cause of vitamin B12 deficiency, the experts agreed that food-cobalamin malabsorption may cause vitamin B12 deficiency in elderly people even if the dietary intake of B12 is adequate and the person has no gastrointestinal disorders. To support identifying the cause of vitamin B12 deficiency, doctors need to inquire whether the person adheres to a diet that is low in foods from animal sources and should ask the person about disease history, regular use of certain medications, and recreational use of nitric oxide. There is agreement that the malabsorption of vitamin B12 can be suspected in people with autoimmune disorders, in patients who have had gastric surgery, in people with a family history of pernicious anemia or with positive test results for serum antibodies against intrinsic factor or parietal cells. Moreover, assessing folate and iron statuses can aid in the differential diagnosis of vitamin B12 deficiency (Table 1). The algorithm for diagnosing vitamin B12 deficiency and its causes was agreed upon among the panelists (Figure 2). In people with symptoms suggesting vitamin B12 deficiency, the general practitioner can collect information on medical history, perform physical examinations, and perform basic

laboratory tests such as full blood cell count and serum B12 concentration. Advanced clinical and laboratory markers can be ordered if there are indications (e.g., intrinsic factor antibodies in cases of gastrointestinal symptoms). After the preliminary workup, treatment with B12 can start. Depending on the clinical symptoms, some patients may need referral to other specialties.

Table 2. Expert consensus was reached after two survey cycles on all of the following topics related to treatment, prophylaxis, and long-term B12 deficiency.

1. 1. At present, it is unclear whether different forms of B12 differ in their effectiveness or safety. Clinical trials comparing the safety and effectiveness of the commercially available forms are needed.
2. 2. Regarding the use of prophylactic B12 supplementation:
3. 3. There is no one-size-fits-all regarding the dose of B12, the frequency and the route of B12 therapy in people with B12 deficiency. Regarding the decision on the route of B12 administration:
4. 4. If B12 treatment fails in symptomatic patients, one or more of the following measures are recommended:
5. 5. B12 deficiency during pregnancy, lactation and in infancy needs to be detected and treated as early as possible because of the serious effects of B12 deficiency on fetal and infant development.
6. 6. Women with a previously diagnosed B12 deficiency or dietary restriction of animal foods should take prophylactic B12 supplementation from pre-pregnancy to the end of the lactation period.

38 0.92 (0.79–0.98)

1 Total number of the panelists who answered each of the questions. 2 Mean percentage and the 95% confidence intervals of the panelists who considered themselves qualified to answer the question and chose “agree” or “strongly agree” to the answer. We considered that a consensus was reached when the lower bound of the 95%confidence intervals is 50% or higher.

1. 3.2.4. Consensus on Clinical Practices of Treatment, Prophylaxis, and Long-Term Management of Vitamin B12 Deficiency
2. 4. Discussion

1. 4.1. Delphi Consensus

The present work was undertaken with the aim of reviewing the current knowledge related to the diagnosis and treatment of vitamin B12 deficiency. In addition, we sought expert opinion to guide the diagnosis and treatment of vitamin B12 deficiency, especially in areas where there are still heterogeneous views and practices. This study identified controversial topics that need to be investigated in future studies.

Our results suggest that introducing educational elements for healthcare professionals and patients could shorten the path for diagnosing vitamin B12 deficiency and accelerate the initiation of treatment. The need to use different laboratory markers of vitamin B12 to aid in diagnosis stresses the importance of making these markers widely available and affordable, which is not the case in many countries. On the other hand, to avoid costs for the healthcare system, measuring vitamin B12 biomarkers needs to be tailored to the patient’s health condition. Furthermore, the regular measurement of serum vitamin B12 concentrations in all patients at risk (e.g., people using metformin) may cause unnecessary costs in the long term, which needs to be weighed against the costs of vitamin B12 treatment. High serum concentrations of vitamin B12 may be encountered while the clinical picture suggests B12 deficiency. High concentrations of vitamin B12 may be due to underreporting supplement use, autoimmune disorders interfering with the B12 assay, or underlying renal or liver diseases. In addition, some malignancies cause high circulating levels of vitamin B12 and may thereby impact the interpretation of this marker in the context of diagnosing vitamin B12 deficiency [92]. In this case, the concentrations of methylmalonic acid or homocysteine can provide clues on intracellular vitamin B12 status.

The most valuable source for identifying the cause of vitamin B12 deficiency is listening to patients’ complaints, disease history, and clinical examination. Symptoms affecting the

nervous system or mental function are more difficult to diagnose and may escape detection due to the low specificity of the symptoms and the limited time available for each patient in primary care settings.

Identifying the cause of vitamin B12 deficiency would enable tailoring the treatment with vitamin B12 (dose, frequency, route of administration, and duration). In people with severe signs and symptoms, the use of injectable forms of vitamin B12 for several weeks is acknowledged, at least in the initial treatment phase. The therapeutic regimen can be revised later when symptoms improve or when patients need to receive vitamin B12 for a longer duration. Prophylactic use of vitamins should receive special attention in at-risk groups and during critical life stages, such as pregnancy and lactation, or in elderly individuals.

1. 4.2. Additional Points Raised in the Board Discussion

The board members agreed that in patients with clinically suspected severe B12 deficiency, there must not be any delay in initiating appropriate B12 treatment. Serum specimens for measuring vitamin B12 marker(s) should be collected prior to treatment. Laboratory confirmation of the deficiency can help achieve coverage of B12 treatment costs by health insurance in many countries.

The board discussed that measuring serum B12 concentrations to monitor B12 treatment should be decided on a case-by-case basis (for example, when people show new symptoms, to check compliance with oral treatment, and to check whether B12 was absorbed after oral administration). Although one-third of patients with vitamin B12 deficiency can have normal serum B12 concentrations, measuring serum vitamin B12 is still a convenient screening test when the clinical picture is suggestive of vitamin B12 deficiency. The use of holotranscobalamin as a screening marker for B12 deficiency may increase the cost of the investigations.

The use of vitamin B12 as a prophylactic measure in patients with atrophic gastritis, after bariatric surgery, in vegans, and due to illnesses or medications has reached the consensus of the panelists. The board members highlighted the importance of considering prophylactic vitamin B12 in people using metformin [93] or L-DOPA [94,95] to reduce the possible increased risk of neuropathy due to vitamin B12 deficiency, although this needs to be tested in randomized controlled trials.

There is currently no gold standard for choosing the dose and route of B12 administration. Various protocols have been used successfully. In general, whenever B12 deficiency is clinically manifested or the patient cannot absorb B12, therapeutic doses between 1000 µg/day and 2000 µg/day orally or 1000 µg i.m. (e.g., daily, then weekly, then monthly for maintenance treatment) can be used. The severity of the deficiency symptoms may necessitate choosing injectable forms of B12, at least in the starting phase. The clinical response to B12 treatment in SCD patients is expected to be better when large doses of B12 are administered more frequently than when B12 is administered less frequently [96]. The treatment regimen can be revised later to both fulfill the treatment goals and be convenient for patients.

The scientific board members noted that the duration needed to resolve symptoms of vitamin B12 deficiency can vary. The lack of clinical improvement after 4–8 weeks for anemia and after 6–12 months for neurological signs could suggest that the symptoms are not due to B12 deficiency or that the dose of vitamin B12 or the route of administration needs to be adjusted to the severity of symptoms. Since serum B12 concentrations do not always mirror the clinical picture, this marker is not optimally suited to monitor the effect of treatment, although it can help uncover a lack of patient compliance and malabsorption of oral B12 treatment. An insufficient clinical response to B12 treatment during the first weeks of therapy should not routinely lead to the discontinuation of treatment.

1. 4.3. Strengths and Limitations
2. 4.4. Conclusions

The present study provides an overview of consistent data on the diagnosis and treatment of vitamin B12 deficiency. In addition, the Delphi study established a robust consensus on various aspects of diagnosing and treating B12 deficiency to support medical practice in areas where there is insufficient evidence. The experts agreed on the need for educational and organizational changes in the current practices. Although clinical symptoms should receive more weight in diagnosing B12 deficiency, the panelists recognized the need to use serum vitamin B12 concentrations as a cost-effective screening marker and the need to additionally measure a metabolic marker to support the diagnosis. The B12 dose and treatment regimens need to be adjusted according to the severity of the symptoms and the cause of the deficiency. Several topics require future in-depth investigations, such as the clinical benefit of using prophylactic B12 supplementation in some groups who are at risk of B12 deficiency due to accompanying diseases or medications.

Supplementary Materials: The following supporting information can be downloaded at: https:// www.mdpi.com/article/10.3390/jcm13082176/s1, Figure S1: Study Flow Diagram; Figure S2: The composition of the 42 panelists who took part in both survey rounds; Figure S3: Vitamin B12 deficiency may cause or be associated with signs and symptoms in multiple organ systems. The crude order of affected systems is shown in the figure from highest prevalence to lowest prevalence according to panelists’ votes in survey 1. Table S1: Keywords and filters used in the literature search in PubMed; Table S2: The inclusion and exclusion criteria used in the scoping review; Table S3: Search results, included and excluded studies in the full-text stage, and the reasons for the exclusions; Table S4: Questions, potential answers, and results of survey 1 and the answers that were qualified for the second Delphi round (survey 2) according to the study criteria; Table S5: Questions included in Delphi survey 2 and the results of agreement or disagreement; Table S6: Topics on vitamin B12 deficiency with consistent results across studies in the literature; Table S7: Topics related to the diagnosis and treatment of vitamin B12 deficiency that did not achieve consensus of the panelists according to the study criteria.

Author Contributions: R.O. and K.R., planning, design, conduct, critical input at all stages of the study, and interpretation; R.O., data analysis and writing the first draft of the manuscript. All authors contributed equally to developing the surveys, interpreting the results, and overall discussion and provided critical input to the manuscript. All authors have read and agreed to the published version of the manuscript.

Funding: The study was funded by Wörwag Pharma, Germany (grant number: not applicable). The company had no role in designing the study, running the surveys, analyzing and interpreting the data, or drafting the manuscript.

Institutional Review Board Statement: Not applicable. Informed Consent Statement: Not applicable.

Data Availability Statement: The data that support the findings of this study are available from the corresponding author upon reasonable request.

Acknowledgments: The authors would like to thank Wörwag Pharma for making the present work possible. The skillful support of Jana Golombek and Lena Klusik in the organization and technical conduct of the surveys is gratefully acknowledged. We thank the 46 panelists for taking part in the survey. Their enthusiasm, dedication, and objective comments in answering the comprehensive sets of questions in both survey rounds comprise the basis for this consensus. The Vitamin B12 Consensus Panelists Group included: 1. Agata Sobczyn´ska-Malefora, Nutristasis Unit, Haemostasis & Thrombosis, St. Thomas’ Hospital, London, UK. 2. Aleksandra Araszkiewicz, Poznan University of Medical Sciences, Poland. 3. Andrew McCaddon, Faculty of Social and Life Sciences, Wrexham University, Wrexham, UK. 4. Anne M Molloy, Trinity College Dublin, Ireland. 5. Bruce H.R. Wolffenbuttel, Department of Endocrinology, University Medical Center Groningen, 9700 RB Groningen, The Netherlands. 6. Bruno Annibale, Department of Medical Surgical and Translational, Medicine Sapienza University, Rome, Italy. 7. Christine A.F. von Arnim, Department of Geriatrics, University Medical Center Göttingen, Germany. 8. Christy C Tangney, FACN, CNS, Departments of Clinical Nutrition & Preventive Medicine, Rush University Medical Center, 600 S Paulina St, Room 716 ACC, Chicago, USA. 9. David Smith, Department of Pharmacology, University of Oxford, Oxford, UK. 10. Dinh Tung Do, Hanoi Saint Paul Hospital, Vietnam. 11. Dongming Zheng, Department of Neurology, Shengjing Hospital of China Medical University, China. 12. Edith Lahner, Sapienza University of Rome, Department of Medical-surgical sciences and translational medicine, Italy. 13. Gabriela Spulber, Clinical geriatrics, Karolinska Institutet, Sweden. 14. Georgeta Daniela Georgescu, Carol Davila University of Medicine and Pharmacy, Bucharest, Romania. 15. Francesca Mangialasche, Karolinska Institutet, Center for Alzheimer Research, Sweden. 16. Hendrika (H.J.M.) Smelt, Obesity Center, Catharina Hospital Eindhoven, The Netherlands. 17. Janet B McGill, Washington University School of Medicine, 660 S. Euclid, Campus Box 8127, St. Louis, MO 63110, USA. 18. J. David Spence, Neurology & Clinical Pharmacology, Western University, and Director, Stroke Prevention & Atherosclerosis Research Centre, Robarts Research Institute, London, ON, Canada. 19. John Killen, Macquarie Medical School Sydney, Australia. 20. P Julian Owen, Department of Trauma and Orthopaedics, Addenbrooke’s, Cambridge University Hospitals NHS Trust, Cambridge, UK. 21. Lisette CPGM de Groot, Wageningen University, The Netherlands. 22. Michelle Murphy, Faculty of Medicine & Health Sciences, Universitat Rovira i Virgili, Spain. 23. G Bhanuprakash Reddy, ICMR-National Institute of Nutrition, Hyderabad-500007, India. 24. Pradeepa Rajendra, Madras Diabetes Research Foundation, Chennai, India. 25. Ralph Green, University of California, Davis Medical Center. 26. Sadanand Naik, K.E.M. Hospital, Pune, India. 27. Tsvetalina Tankova, Medical University, Sofia, Bulgaria. 28. William Huynh, Randwick Clinical Campus, UNSW Medicine and Health; FMH Translation Research Collective, Faculty of Medicine and Health, University of Sydney; and Prince of Wales Hospital, Southern Neurology, Kogarah NSW, Sydney, Australia. 29. Wolfgang N. Löscher, Department of Neurology, Medical University Innsbruck, Austria. 30. Zyta Beata Wojszel, Department of Geriatrics, Medical University of Bialystok, Poland. The remaining 16 panelists chose not to disclose their names in the article.

Conflicts of Interest: All authors received consulting fees and travel costs from Wörwag Pharma in relation to their role in this study. JS lectured and consulted for TEVA, AbbVie, Ipsen, Roche, Novartis, Biogen, Novo Nordisk, Sanofi, Takeda, and Amicus. RC received institutional grants from Amgen, Amryt Pharma, Novartis, and Sanofi and received honoraria for consulting and lectures from Amgen, Amryt Pharma, Astra Zeneca, Bayer, Boehringer Ingelheim, ExCEEd Orphan, Sanofi, Zentiva, AOP Orphan, Bayer, Roche, and Servier. AE received support for attending meetings from Amgen and received a consulting honorary from BMS, Pfizer, and Boehringer Ingelheim. The authors declare that Wörwag Pharma paid for study materials, scientific editing, and article processing charges.