In Reply

[摘要] Requests for the determination of vitamin B12 (B12) status remain a clinical reality but current laboratory methods for this have limitations (1). In recent years, measurement of holotranscobalamin (holoTC), the fraction of B12 that can enter cells, has been proposed as an improvement, and attempts to demonstrate this improvement have used increased serum methylmalonic acid (MMA) and/or total homocysteine (tHcy) as indicators of deficiency of B12. Both MMA and tHcy may be compromised by renal function and other factors, particularly in an elderly population. The clinical utility and analytical aspects of holoTC have recently been reviewed (2) and current evidence merits continued study of the marker, both for diagnosis of B12 deficiency and assessment of vitamin B12 status.We investigated indicators of B12 status in an elderly population and used low red cell B12 concentrations (RBC-B12) as a biologically different standard of deficiency. Carmel makes several points regarding the shortcomings of B12 status assays and we agree that these extend to RBC-B12. We do not suggest RBC-B12 has a routine role. However, we observed correlations between RBC-B12 and the B12 …

[学科分类] 过敏症与临床免疫学