Commutability of NIST SRM 1955 Homocysteine and Folate in Frozen Human Serum with selected total homocysteine immunoassays and enzymatic assays

BackgroundThe National Institute of Standards and Technology (NIST) has recently developed Standard Reference Material (SRM) 1955 Homocysteine and Folate in Frozen Human Serum with certified values for total homocysteine (tHcy) and 5-methyl-tetrahydrofolic acid. NIST has performed an international, interlaboratory assessment of SRM 1955 commutability; results are reported for tHcy only.MethodsTotal Hcy was measured in 20 patient sera and in 3 levels of SRM 1955 using 14 immunoassays and/or enzymatic assays. Liquid chromatography/tandem mass spectrometry was utilized as the reference assay. An “errors-in-variables” statistical model was utilized to assess the commutability of SRM 1955.ResultsNormalized residuals ranged from − 2.65 to 2.19 for SRM 1955. The median interlaboratory/interassay imprecision (CV) was ≈ 4% for patient specimens and ranged from ≈ 3% to ≈ 7% for SRM 1955. The median intra-assay imprecision ranged from ≈ 1% to ≈ 13%. Orthogonal residuals, as a descriptor of assay accuracy, ranged from 0.29 to 7.71 and from 0.20 to 2.22 for patient specimens and SRM 1955 samples, respectively.ConclusionThe current study suggests that SRM 1955 is commutable with the investigated tHcy assays; however, a broader specimen set needs to be evaluated to completely substantiate this conclusion.