The importance of active B12 (holotranscobalamin) measurement in the diagnosis of vitamin B12 deficiency in type 2 DM patients using metformin

B12 deficiency, which can be seen in type 2 DM patients using metformin, can cause peripheral nerve damage that can easily be confused with peripheral neuropathy, a complication of diabetes. Therefore, early diagnosis is important in patients. In our study, we aimed to investigate benefit of Active B12 measurement in diagnosing B12 deficiency, as it might be a better alternative in follow-up of B12 levels in type 2 DM patients using metformin. Patients were divided into three groups according to their Total B12 levels: Deficient, Borderline and Sufficient. Homocysteine and Active B12 (holotranscobalamin) levels were studied with Chemiluminescent Microparticle Immunoassay (CMIA) for quantitative determination. Duration of use, daily metformin dose, and other parameters were collected from records and interviews. A statistically significant positive correlation was found between Total B12 and Active B12 (r = 0.624, p = 0.000). A statistically significant negative correlation was found between metformin dose and Active B12 and Total B12 levels (r = -0.309, r = -0.212, respectively; p < 0.05). While effects of metformin dose and duration of use groups were not found statistically significant in binary logistic regression analysis for Total B12 groups, the OR value for Active B12 was found to be 5.575 (95% CI 1.456–21.343, p = 0.012). It is important to closely follow up Type2 DM patients with high daily metformin dose in terms of B12 deficiency. Active B12 is a significant predictor of B12 deficiency compared to other parameters.