Levels of holo-transcobalamin are more closely associated with pernicious anaemia than total B12 levels

Abstract

<h3>Aims</h3> Vitamin B12 deficiency is usually due to dietary factors, however clinicians always consider the possibility of autoimmune pernicious anaemia. The Schillings test is no longer routinely available and therefore diagnosis often includes the specific intrinsic factor auto-antibodies (IFAb) +/– parietal cell auto-antibodies (PCAb). Holo-transcobalamin (HoloTC), also known as active B12, has proved to be a more reliable indicator of B12 deficiency than measuring total B12 (TB12). We therefore reviewed our experience with this test to see if HoloTC was more closely associated with pernicious anaemia testing. <h3>Methods</h3> We reviewed 1359 patients where HoloTC +/– TB12 was measured as well as one or more of IFAb and PCAb. We used each patient's first B12 result(s) for the analysis. HoloTC was measured by Abbott AxSym and total B12 was measured by Abbott Architect. PCAb antibodies are detected by immunofluor-escence whereas IFAb are measured by Alegria automated ELISA. <h3>Results</h3> When HoloTC was very low (<10pmol/L), 21% of patients had positive IFAb and 42% had positive PCAb. When HoloTC was mildly low (10–22pmol/L), 8% had positive IFAb and 18% had positive PCAb. For very low TB12 (<100pmol/L), 8% had positive IFAb and 24% had positive PCAb. When TB12 was mildly low (100–149pmol/L), 4% had positive IFAb and 11% had positive PCAb. <h3>Conclusions</h3> PCAb were more likely to be positive at any B12 level consistent with its known poor specificity. The more specific IFAb positivity is more likely to be associated with low HoloTC levels than low TB12 levels.