Failure of the holotranscobalamin assay in vitamin B12-deficient patients

Abstract

AbstractBackgroundIt has been demonstrated that vitamin B12 determinations fail, especially in patients with pernicious anemia with high titers of intrinsic factor antibody. Consistent with this finding, we observed a case of falsely normal holotranscobalamin (HoloTC) results in a patient with pernicious anemia and severe vitamin B12 deficiency. We aimed to investigate whether such a situation can also be seen in other individuals.MethodsWithin the frameworks of the SENIORLAB study and routine samples from a mixed patient population referred to a laboratory for investigation of B12 status, we searched for study participants displaying a normal HoloTC level (≥50 pmol/L) together with a decreased total vitamin B12 level (<125 pmol/L). Thereafter, we determined whether samples with discrepant biochemical markers (i.e. low vitamin B12, normal HoloTC) also had increased functional markers of vitamin B12 deficiency (methyl malonic acid [MMA], homocysteine [Hcy]) and/or a low value of Fedosov’s combined indicator of vitamin B12 status (<−0.5).ResultsThe prevalence of a normal HoloTC level and low total vitamin B12 level among the group of healthy seniors (n=1451) was 0.21% (95% confidence interval [CI], CI, 0.08–0.6%). Among the 106,635 routine samples with concurrent HoloTC and total vitamin B12 determination, 176 (i.e. 0.17%, 95% CI, 0.14–0.19%) had discrepant biochemical markers. Among them, 24 who were identified as having discrepant biochemical markers and a diagnosis of vitamin B12 deficiency could be confirmed with functional markers.ConclusionsInitial and isolated screening for vitamin B12 deficiency using a HoloTC cut-off of ≥50 pmol/L in a small subset of patients may reveal false-negative (normal) results, meaning that patients with vitamin B12 deficiency may remain undetected.