Revisiting the effects of spectral interfering substances in optical end-point coagulation assays.

INTRODUCTION: Hemolysis, icterus, and lipemia (HIL) are common pre-analytical variables in the clinical laboratory. Understanding their effects on coagulation laboratory results is essential. METHODS: HIL 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. RESULTS: Hemolysis (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. CONCLUSIONS: Verification of the manufacturer's recommended interference thresholds is important since it may avoid inappropriate instrument flagging and/ or sample rejection.

An In Silico Exploration of the Factors That Affect the Precision of the Bethesda Assay.

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.

Clinical and laboratory diagnosis of autoimmune factor V inhibitors: A single institutional experience.

BACKGROUND: Coagulation factor V inhibitors (FV-i) may occur in patients with congenital FV deficiency or previously hemostatically normal patients (autoimmune (AI)-FV-i). Most of the published literature is confined to case reports. OBJECTIVE: Describe clinical and laboratory features of AI-FV-i identified through the Special Coagulation Laboratory at Mayo Clinic, Rochester, Minnesota. METHODS: In this retrospective study individuals with FV-i screens performed from January 1999 to February 2017 were identified through the special coagulation laboratory database. Clinical presentation, management, and outcomes were collected for our institutional patients while detailed laboratory data was collected for all tested patients. RESULTS: Of patients with FV-i managed at our institution, 2/8 (25%) patients experienced no bleeding. There was no correlation between inhibitor titers and/or FV activity (FV:C) levels and clinical bleeding. Hemostatic management included fresh frozen plasma, platelet transfusion, activated prothrombin complex concentrates, and recombinant factor VIIa. Only 2 patients received immunomodulatory treatment. FV-i mixing studies with normal pooled plasma (n = 26) demonstrated inhibition on immediate mix but progressive inhibition after 1 h of incubation could not be demonstrated. 71% of platelet neutralization procedures were falsely positive while 59% of DRVVT assays were indeterminate. CONCLUSION: FV-i demonstrates immediate inhibition on mixing studies; however our limited data does not support a time dependent inhibition. Our clinical cohort confirms the variable clinical phenotype for individuals with FV-i and supports the notion that management of FV-i should be guided by clinical symptoms and not FV:C or FV-i titer.

Clinical importance of positive test results for lupus anticoagulant and anticardiolipin antibodies.

OBJECTIVES: To assess the performance of 4 clotting assays for lupus anticoagulant (LA) detection, to determine the prevalence of LA and anticardiolipin antibodies (aCL), and to correlate LA and aCL prevalence with systemic disease and thrombosis. PATIENTS AND METHODS: We studied 664 consecutive patients at the Mayo Clinic in Rochester, Minn, who were referred for laboratory testing because of a clinical suspicion of LA or thrombophilia between June 25, 1990, and July 1, 1991. RESULTS: Of 664 patients tested for LA, 584 also were tested for aCL. Of patients tested for both LA and aCL, 137 (235%) had positive results for one or both tests (13 [95%], LA-positive only; 76 [555%], aCL-positive only; and 48 [35.0%], positive for both). The dilute Russell viper venom time (DRVVT) was the most frequently positive LA assay (74% of the 61 patients with positive results for LA). Twenty-two patients (36.1% of the 61) had positive results for all 4 LA assays, whereas 21 (34.4% of the 61) had positive results for only 1 LA assay: activated partial thromboplastin time (3 patients [4.9%]), plasma clot time (5 patients [8.2%]), kaolin clot time (5 patients [8.2%]), or DRVVT (8 patients [13.1%]). Thromboembolism prevalence was not definitely associated with positive test results (LA only, aCL only, or LA plus aCL), nor was it strongly associated with aCL isotype or titer. Furthermore, thromboembolism prevalence was not increased when all LA assays were positive, although a history of deep venous thrombosis or pulmonary embolism was nonsignificantly associated with positive results for all 4 LA tests. The likelihood of having both LA- and aCL-positive test results was higher among patients with systemic lupus erythematosus (26 [19.0%] of 137 patients with positive results for one or both tests), but they had no more thrombotic events or fetal loss than other patients in our study group. CONCLUSIONS: The DRVVT identified more patients with LA than the other LA tests, but more than 1 LA test was required to identify all patients with LA. Positive results were much more common for aCL than for LA. No single LA test or anticardiolipin isotype correlated with thrombosis or systemic disease in this population.