Vitamin B6 Deficiency May Not Always Present As Microcytic Hypochromic Anemia

Objective Vitamin B6 (VB6) deficiency leads to microcytic hypochromic anemia with ringed sideroblasts. Sideroblastic anemia due to VB6 deficiency is an important differential diagnosis to consider in cases with sideroblastic anemia associated with myelodysplastic syndrome (MDS). However, VB6 screening is underutilized in Japan as it is not covered by the national health insurance system, potentially leading to low screening rates. Methods This study retrospectively evaluated the relationships between VB6 (pyridoxal (PAL)) and other clinical parameters, including anemia, with univariate and multivariate regression analysis. Among 43 patients, we excluded one case where vitamin B6 supplementation had already started before blood sampling. We enrolled 42 patients who had undergone measurement of VB6 level (PAL) at Toho University Sakura Medical Center (Sakura, JPN) between September 2010 and October 2023. Results The PAL levels were significantly correlated with mean corpuscular volume (MCV) and mean corpuscular hemoglobin (MCH). Mean corpuscular hemoglobin concentration (MCHC) and vitamin B12 (VB12) also tended to correlate positively with PAL; however, no correlation was observed between PAL levels and other parameters. The PAL was positively correlated only with MCV and MCH in the subgroup analysis of hematological disorders alone. Only alkaline phosphatase (ALP) showed a significant decrease in the PAL <6 ng/mL group compared with the PAL ≥6 ng/mL groups; no significant differences were observed in RBCs, hemoglobin (Hgb), MCV, MCH, or MCHC between the PAL <6 and ≥6 ng/mL groups in both the overall cohort of 42 patients and the subset of 12 patients with hematological disease. Multivariate regression analysis revealed that only RBC and MCV levels independently and significantly affected Hgb levels. Conclusions These findings suggest that anemia due to VB6 deficiency may not always present as microcytic hypochromic anemia. Thus, VB6 deficiency must be included in the differential diagnosis of anemia, especially when there's suspicion for MDS.