Assay interference causing factitious hypervitaminosis D

Abstract

25-hydroxyvitamin D is most commonly measured with the use of automated immunoassay technology. It is well known that immunoassays are prone to interference from immunoglobulins present in the circulation. Here we present a case of a monoclonal IgM paraprotein interference in the Abbott Architect 25-hydroxyvitamin D assay, a quantitative delayed one-step competitive immunoassay using chemiluminescent microparticle immunoassay (CMIA) technology. A 68-year-old female with newly diagnosed lymphoplasmacytic lymphoma / Waldenstrom’s macroglobulinaemia and a monoclonal IgM paraprotein of 44 g/L, had a 25-OH vitamin D measurement of >400 nmol/L on the Abbott Architect 25-hydroxyvitamin D assay. This result was inconsistent with clinical findings. A 1:2-dilution of the sample returned a non-linear 25-OH Vitamin D result of 84 nmol/L suggestive of an interferent present in the sample. The presence of rheumatoid factor was excluded with a measurement below the limit of quantitation of the assay. Referral of the sample for measurement of total 25-hydroxyvitamin D by liquid chromatography-tandem mass spectrometry (LC-MS/MS) returned a result of 75 nmol/L. The sample analysed was collected before the patient started chemotherapy and we concluded that the most likely interferent is the monoclonal IgM paraprotein. References 1. Ong MW, Salota R, Reeman T, et al. Artefactual 25-OH vitamin D concentration in multiple myeloma. Ann Clin Biochem 2017; 54: 716–20. 2. Belaidi N, Georges A, Lacroix I, et al. Hypercalcemia and elevated concentration of vitamin D: A case report too easy to be true. Clin Chim Acta 2016; 457: 123–4.L20048475292020-02-24 <br />