Relationship between glycosylated hemoglobin and vitamin B12 deficiency anemia

OBJECTIVE: Previous studies showed that vitamin B12 deficiency anemia causes a false increase in glycosylated hemoglobin (HbA1c) and that HbA1c decreases with B12 treatment. However, no study has been conducted on how much an increase in hemoglobin (Hgb) level causes a decrease in HbA1c level after treatment. METHODS: The study included 37 patients who were not diagnosed with diabetes, did not use anti-diabetic drugs, were pre-diabetic according to HbA1c level, and were diagnosed with vitamin B12 deficiency anemia in the patient group and 40 healthy volunteers of similar age and gender characteristics in the control group. The patient group was given 1 mg/day of cyanocobalamin (vitamin B12) orally for 3 months. Patients’ Hgb, mean corpuscular volume, fasting plasma glucose, HbA1c, and vitamin B12 values were compared at the beginning and at the end of the 3(rd) month. RESULTS: In the patient group, it was determined that 0.94 mg/dL increase in Hgb after vitamin B12 treatment caused a 0.24 decrease in HbA1c (%). The initial HbA1c of the patient group was 6.01±0.20 and the 3(rd)-month HbA1c was 5.77±0.33; the initial and 3(rd)-month Hgb values were 11.31±0.28 and 12.26±0.33, respectively; the initial and 3(rd)-month vitamin B12 (ng/L) levels were 112.43±7.18 and 408.48±119.61, respectively; and there was a significant difference between the initial and 3(rd)-month values (p<0.001, p<0.001, p<0.001, respectively). Moreover, 35% of the patients in the patient group had no diagnosis of prediabetes according to the HbA1c level at the end of the 3(rd) month. CONCLUSION: Elimination of vitamin B12 deficiency anemia before making a diagnosis or treatment decision according to HbA1c level will prevent patients from misdiagnosis of diabetes and unnecessary treatment changes in diabetic patients.