Screening for metabolic vitamin B12 deficiency by holotranscobalamin in patients suspected of vitamin B12 deficiency: a multicentre study.

Background: Vitamin B(12) deficiency occurs frequently, especially among the elderly. However, screening for vitamin B(12) deficiency is hampered by poor sensitivity of the existing total vitamin B(12) assay. Methylmalonic acid (MMA) is considered as the most representative indicator of metabolic vitamin B(12) deficiency and is used as such in this study.