Cardel, Laynalee

AbstractIntroductionHemolysis, icterus, and lipemia (HIL) are common pre‐analytical variables in the clinical laboratory. Understanding their effects on coagulation laboratory results is essential.MethodsHIL effects on the prothrombin time (PT), activated partial thromboplastin time (APTT), dilute Russell's viper venom time (DRVVT), thrombin time (TT), and protein C chromogenic activity (CFx) were evaluated on the ACL TOP 750 optical analyzer and STA‐R Evolution mechanical analyzer (PT and APTT only) by spiking normal donor, patient, and commercial control samples with varying concentrations of hemolysate, bilirubin, or a lipid emulsion. The relative difference or bias compared to the original results was determined.ResultsHemolysis (H) indices up to 900 mg/dL did not affect the APTT, PT, DRVVT Confirm, TT, and CFx; however, H indices above approximately 200 mg/dL resulted in a false‐negative DRVVT screen and screen/confirm ratio in samples with a lupus anticoagulant. There was an artifactual prolongation of the PT and APTT when conjugated bilirubin was dissolved in aqueous solvents and not when it was dissolved in dimethyl sulfoxide. Icterus (I) indices up to 45 mg/dL did not result in significant (>15%) bias for all assays evaluated. The PT and APTT assays failed to produce a robust clot curve when the lipemia (L) index exceeded 6000 milliabsorbance units (mAbs), and the TT and DRVVT assays failed when the L index exceeded 3000 mAbs; the CFx assay was unaffected by lipemia.ConclusionsVerification of the manufacturer's recommended interference thresholds is important since it may avoid inappropriate instrument flagging and/ or sample rejection.

Abstract Objectives Despite more than 40 years of experience performing the Bethesda assay (BA), poor intra- and interlaboratory precision remains the biggest laboratory challenge to date. Methods The BA procedure was modeled using stochastic simulation techniques to determine the precision of the BA up to dilutions of 1:4,096, to estimate the minimum significant relative change at various inhibitor titers, and to understand the laboratory procedural variables that could significantly affect the performance of the BA at high dilutions. Results Selecting the lowest dilution tube with a residual activity closest to 25% for calculating the reported Bethesda titer (BT), using a factor activity assay with a coefficient of variation less than or equal to 7.5% in the range of 15% to 50% factor activity level, performing the factor activity measurement in replicates, and minimizing pipette volumetric error resulted in the lowest imprecision in the reported BT. The factor neutralization kinetics of the inhibitor appear to have little impact on the precision of the assay if the incubation time is greater than 90 minutes. Conclusions This in silico model will assist future laboratory efforts in standardizing the quantification of specific coagulation factor inhibitors and improving the precision of the reported results.