Effect of delayed processing of whole blood on the stability of vitamin B12, folate and transferrin receptor in human serum

Abstract

As part of a comprehensive assessment of analyte stability in support of international nutrition studies, we compared several analytical methods that use different principles. Vitamin B12: protein binding (Biorad) and immunoassay (Axsym). Folate: protein binding (Biorad) and microbiological (MA) assay. TfR: immuno‐turbidimetry (Hitachi 912) and ELISA (Ramco). To evaluate stability under harsh field conditions, whole blood (WB) collected from healthy volunteers was stored at 32°C for up to 3 days (d) before serum separation. Specimen treatment effects were calculated using relative changes (%) compared with immediately processed WB. Differences > ± 5% were considered significant.Serum B12 levels (n=27) were unchanged using Axsym; an apparent artifact of incubation of WB at 32°C was measured using the Biorad B12 assay. Significant folate (n=16) losses were measured using either method (greater folate losses with MA versus Biorad). Hitachi serum TfR levels (n=35) were unchanged. Using Ramco, TfR levels were slightly more variable. We conclude that apparent analyte ‘stability’ may be method‐dependent, thus multiple methods should be used to verify findings.