Holotranscobalamin -: a first choice assay for diagnosing early vitamin B12 deficiency?

Objectives. The performance of holotransco balamin (holoTC) was compared with the other markers of vitamin B-12 deficiency, and the influence of age, renal function, and thyroid status was examined. Design and interventions. We examined 937 individuals not treated with vitamin B12 but in whom vitamin B12 deficiency was suspected because of a plasma methylmalonic acid (MMA) above 0.28 mu mol L-1 within the past 4 years. Besides laboratory tests, a structured interview and a neurological examination were performed amongst 534 individuals. Amongst these, 140 individuals qualified for a randomized trial (MMA 0.40-2.00 mu mol L-1). They were randomized to injections with vitamin B-12 or placebo and re-examined after 3 months. Setting. One university hospital in Aarhus, Denmark. Results. The ROC curves indicate that holoTC (AUC: 0.90) compared favourable with plasma vitamin B-12 (AUC: 0.85) for identifying individuals likely to have vitamin B12 deficiency (MMA >= 0.75 mu mol L-1 and plasma total homocysteine (tHcy) >= 15 mu mol L-1), and further that holoTC (AUC: 0.91) might replace combined testing with plasma vitamin B-12 and the metabolites. No association was observed between the biochemical markers and symptoms and signs possibly related to vitamin B-12 deficiency. HoloTC, TC saturation, plasma vitamin B-12, MMA, and tHcy were significantly associated with plasma creatinine (all with P < 0.001). Only tHcy was significantly associated with thyroid stimulating hormone (P 0.02). Conclusions. HoloTC shows promise as first-line tests for diagnosing early vitamin B-12 deficiency.