Grebe, Stefan K G

AbstractObjectivesMatrix differences among serum samples from non-pregnant and pregnant patients could bias measurements. Standard Reference Material 1949, Frozen Human Prenatal Serum, was developed to provide a quality assurance material for the measurement of hormones and nutritional elements throughout pregnancy.MethodsSerum from non-pregnant women and women in each trimester were bottled into four levels based on pregnancy status and trimester. Liquid chromatography tandem mass spectrometry (LC-MS/MS) methods were developed and applied to the measurement of thyroid hormones, vitamin D metabolites, and vitamin D-binding protein (VDBP). Copper, selenium, and zinc measurements were conducted by inductively coupled plasma dynamic reaction cell MS. Thyroid stimulating hormone (TSH), thyroglobulin (Tg), and thyroglobulin antibody concentrations were analyzed using immunoassays and LC-MS/MS (Tg only).ResultsCertified values for thyroxine and triiodothyronine, reference values for vitamin D metabolites, VDBP, selenium, copper, and zinc, and information values for reverse triiodothyronine, TSH, Tg, and Tg antibodies were assigned. Significant differences in serum concentrations were evident for all analytes across the four levels (p≤0.003).TSH measurements were significantly different (p<0.0001) among research-only immunoassays. Tg concentrations were elevated in research-only immunoassays vs. Federal Drug Administration-approved automated immunoassay and LC-MS/MS. Presence of Tg antibodies increased differences between automated immunoassay and LC-MS/MS.ConclusionsThe analyte concentrations’ changes consistent with the literature and the demonstration of matrix interferences in immunoassay Tg measurements indicate the functionality of this material by providing a relevant matrix-matched reference material for the different stages of pregnancy.

AbstractBACKGROUNDDroplet digital PCR (ddPCR) is an emerging technology for quantitative cell-free DNA oncology applications. However, assay performance criteria must be established in a standardized manner to harness this potential. We reasoned that standard protocols used in clinical chemistry assay validation should be able to fill this need.METHODSWe validated KRAS, EGFR, and BRAF quantitative ddPCR assays based on the Clinical Laboratory Improvement Act regulations for laboratory-developed tests in clinical chemistry and the matching Clinical and Laboratory Standards Institute guidelines. This included evaluation of limit of the blank (LOB), limit of detection (LOD), limit of quantification (LOQ), intraassay and interassay imprecision, analytical range, dilution linearity, accuracy (including comparison with orthogonal platforms), reference range study, interference, and stability studies.RESULTSFor the ddPCR assays, the LOB was 4 mutant copies, LODs were 12 to 22 copies, and LOQs were 35 to 64 copies. The upper limit of the dynamic range was 30000 copies, and dilutions were linear down to the LOQs with good accuracy of spike recovery of Horizon reference material. Method comparisons with next-generation sequencing and an alternative ddPCR platform showed complete qualitative agreement and quantitative concordance, with slopes of 0.73 to 0.97 and R2s of 0.83 to 0.99. No substantial interferences were discovered. Wild-type copy numbers in plasma ranged from 462 to 6169/mL in healthy individuals.CONCLUSIONSStandard clinical chemistry assay validation protocols can be applied to quantitative ddPCR assays. This should facilitate comparison of the performance of different assays and allow establishment of minimal significant change thresholds in monitoring applications.