Lupus anticoagulant testing using two parallel methods detects additional cases and predicts persistent positivity.

BACKGROUND: Antiphospholipid antibody syndrome (APS) is characterized by laboratory evidence of antiphospholipid antibodies (aPL) [e.g. lupus anticoagulant (LA), anticardiolipin (ACL), and/or antiß2-glycoprotein I (aB2GPI)] in a clinical setting of thrombosis or pregnancy morbidity. The International Society on Thrombosis and Haemostasis recommends two different testing modalities to detect LA. To evaluate these recommendations in a clinical setting, our hospital, a tertiary care center with a specialized coagulation laboratory, added the dilute Russell's viper venom time to be performed in parallel with the PTT-lupus anticoagulant to detect LA. METHODS: Results of aPL testing were collected on all patients who had LA testing for one year. Chart review was performed to correlate LA results with ACL, aB2GPI, and clinical history. RESULTS: Patients who were initially LA positive by both PTT-lupus anticoagulant and dilute Russell's viper venom time were more likely to be persistently positive. Patients who were positive for ACL and aB2GPI were likely to be positive by both LA methodologies. No single method was absolutely sensitive, as cases of APS were detected by PTTLA only, DRVVT only, and both methods. CONCLUSIONS: The addition of a second testing method for LA provides additional diagnostic information and may be helpful in stratifying risk of thrombosis.

Failure of recombinant factor VIIa to correct the coagulopathy in a case of severe postpartum hemorrhage.

BACKGROUND: Postpartum hemorrhage (PPH)remains an important cause of maternal morbidity and mortality. Several published reports suggest that recombinant factor VIIa (rFVIIa) is effective in controlling bleeding in PPH. This study reports a case of severe PPH complicated by disseminated intravascular coagulation(DIC), in which early rFVIIa (44 mg/kg) administration not only failed to control the bleeding in vivo but also, surprisingly, failed to correct the patient's international normalized ratio (INR) in vitro. It was hypothesized that the failure of rFVIIa to correct the INR indicated a deficiency in a downstream coagulation factor(s). To investigate this, coagulation factor levels were measured in blood samples that had been drawn periodically during resuscitation in the operating room. STUDY DESIGN AND METHODS: Clinical and laboratory data were extracted from the medical record.Plasma samples that had been obtained during resuscitation were frozen, and activity levels of the following factors were subsequently measured: fibrinogen, FII, FV, FVII, F IX, and FX. RESULTS: After rFVIIa administration, the patient's INR remained elevated at 1.9, and bleeding continued. It was determined that at the time rFVIIa was administered, the patient's fibrinogen level was very low(60 mg/dL). INR normalization and control of bleeding was achieved only after the patient's fibrinogen level was restored to normal. FII, F IX, and FX remained at hemostatic levels throughout resuscitation. CONCLUSIONS: In this case of severe PPH complicated by DIC, fibrinogen appears to have been limiting at the time rFVIIa was administered. It is suggested that fibrinogen levels should be corrected during PPH resuscitation before rFVIIa use is considered.

An improved algorithm for activated protein C resistance and factor V Leiden screening.

OBJECTIVES: To evaluate the performance of a Russell viper venom-based activated protein C resistance (APCR) screening test relative to DNA analysis for the factor V Leiden mutation. METHODS: We evaluated the concordance between Pefakit APCR screening results and DNA analysis for 435 patients homozygous (n = 11), heterozygous (n = 310), or wild-type (n =114) for the G1691A allele. RESULTS: Using receiver operating characteristic analysis, we found that a cutoff of 1.89 for the APCR ratio yields a sensitivity and specificity of 99.1%. In patients with discrepant genotype-phenotype correlation, their APCR may provide a more clinically relevant result. CONCLUSIONS: We compared several strategies for employing reflex testing and found that performing initial APCR screening followed by confirmatory molecular analysis on a subset of cases in the borderline regions between the diagnostic groups can reduce unnecessary testing by approximately 80% without compromising diagnostic accuracy.

Impact of an immunoglobulin G-specific enzyme-linked immunosorbent assay on the management of heparin-induced thrombocytopenia.

STUDY OBJECTIVE: To evaluate whether using an immunoglobulin G (IgG)-specific platelet factor 4 (PF4) test reduces the rate of positive PF4 results and has an impact on prescribing practices of nonheparin anticoagulants (direct thrombin inhibitors and fondaparinux) in patients assessed for heparin-induced thrombocytopenia (HIT). DESIGN: Single-center prospective cohort study with a historical control group. SETTING: Large academic medical center. PATIENTS: A total of 672 patients assessed for HIT. INTERVENTION: Patients were assessed for HIT by using either an IgG-specific PF4 enzyme-linked immunosorbent assay (ELISA; 336 patients) or a nonspecific PF4 ELISA (336 patients; historical control group). MEASUREMENTS AND MAIN RESULTS: No significant difference was noted in the proportion of patients with a low, intermediate, or high risk of HIT based on the 4Ts pretest clinical scoring system. The PF4 ELISA was positive in 6.9% versus 11.3% of patients (p=0.04) in the IgG-specific and nonspecific cohorts, respectively. A smaller proportion of patients were prescribed a direct thrombin inhibitor in the IgG-specific cohort (19.4% vs 25.9%; p=0.04). No significant difference in fondaparinux use was noted between the cohorts. The duration of direct thrombin inhibitor therapy, bleeding events, hospital length of stay, and in-hospital mortality was similar in both cohorts. CONCLUSION: Use of an IgG-specific PF4 ELISA was associated with a lower rate of positive PF4 test results. Direct thrombin inhibitor prescribing was also significantly lower during the time period where the IgG-specific PF4 ELISA was used, with no significant differences noted in safety outcomes.

Comparison of Russell viper venom-based and activated partial thromboplastin time-based screening assays for resistance to activated protein C.

Thrombotic disease is a significant cause of mortality and morbidity, with an estimated lifetime risk of greater than 10% in Western populations. One of the most common hereditary thrombophilias is the factor V Leiden mutation, which is identified with a screening assay for activated protein C (APC) resistance and confirmed by DNA analysis. In this study, we compared the commercially available Pefakit (Pentapharm, Basel, Switzerland) and Cryocheck (Precision BioLogic, Dartmouth, Canada) assays, 2 recently developed Russell viper venom (RVV)-based screening tests, with the activated partial thromboplastin time (aPTT)-based screening test currently used in our hospital's clinical laboratory. We found that the aPTT-based assay for resistance to APC had a sensitivity of 100%, a specificity of 70%, and a positive predictive value (PPV) of 70%, whereas both of the RVV-based assays exhibited high sensitivity, specificity, and PPV at 100%. In addition, we found that these new functional assays are more cost-effective relative to the screening algorithm previously used in our clinical laboratory and could potentially eliminate the need for DNA analysis, although further study is required.