Presence of direct thrombin inhibitors can affect the results and interpretation of lupus anticoagulant testing.

Department of Pathology, Pritzker School of Medicine, the University of Chicago, Chicago, IL 60637, USA.
American Journal of Clinical Pathology (Impact Factor: 3.01). 11/2005; 124(4):586-93. DOI: 10.1309/7RYUN5DRK4WCH3PM
Source: PubMed

ABSTRACT In vitro experiments were conducted to determine whether the direct thrombin inhibitors argatroban and lepirudin can interfere with the results of lupus anticoagulant (LA) testing. Concentration-response curves were generated to calculate the concentration of anticoagulant that prolongs the activated partial thromboplastin time (aPTT) to 75 seconds (2.5 times the baseline average). Corresponding concentrations of anticoagulant were added to plasma samples before running dilute Russell viper venom tests (DRVVTs) and LA-sensitive aPTTs (PTT-LAs). Because the DRVVT test system contains an antiheparin agent, DRVVT results were not prolonged in the presence of heparin. With argatroban added to normal plasma samples, neither the DRVVT percent correction of ratio nor the DRVVT test/confirm ratio were elevated, but when added to LA-positive plasma, some false-negative results were observed. Lepirudin increased the DRVVT percent correction of ratio and the DRVVT test/confirm ratio into a range that could lead to false-positive identifications of LAs. In sharp contrast to the DRVVT test system, distinction between LA-positive and LA-negative plasma samples was maintained and possibly even enhanced in the platelet neutralization procedure correction phase of the PTT-LA test system.

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    ABSTRACT: Oral direct thrombin and Xa inhibitors are worldwide distributed for prevention and treatment of thrombosis. It is important to recognize their effects on lupus anticoagulant (LA) testing. The aim of the study is to describe the rate of false-positive results of LA tests on plasmas of patients with previous negative LA tests results that receive dabigatran etexilate (DAB) 110 mg/twice a day, rivaroxaban (RIV) 10 mg/day or 15 mg/twice a day, or enoxaparin 40 mg/day. Blood was taken between 1.5 and 4 h post administration. Tests evaluated are as follows: prothrombin time, APTT, dilute Russell viper venom time (DRVVT) screen, APTT, and DRVVT mixing studies, index of circulating anticoagulant (ICA) with normal plasma, screen/confirm normalized ratio (NR) for DRVVT and silica clotting time (SCT). Plasmas from patients taking DAB (n = 22) presented 100% prolonged APTT and DRVVT with ICA above the cutoff point and 81.8% positive screen/confirm NR, 100% prolonged SCT screen, but 4.5% positive confirmatory NR. All patients receiving RIV at 15 mg/twice a day (n = 4) presented positive DRVVT screen, mixing, and confirmatory tests, 75% and 100% prolonged APTT and SCT screen, with negative screen/confirm NR. Those taking RIV 10 mg/day (n = 22) showed 81.8% prolonged DRVVT screen, 82.3% and 76.5% of them with positive mixing and confirmatory studies. Patients receiving enoxaparin also presented high prevalence of APTT and DRVVT false-positive results. Dabigatran etexilate, RIV, and enoxaparin affect tests for LA not only in screening and mixing, but also in confirmatory studies. We considered that LA testing should not to be performed when patients are taken these drugs, particularly if blood is collected at peak, in order to avoid false-positive results.
    International journal of laboratory hematology 09/2013; 36(2). DOI:10.1111/ijlh.12138 · 1.87 Impact Factor
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    ABSTRACT: Context.-Lupus anticoagulant (LA) is a heterogeneous group of antiphospholipid antibodies. Among others, diluted prothrombin time (dPT) is a sensitive screening test for LA; however, the interpretation of LA tests is difficult in patients treated with anticoagulants. The effect of different types of anticoagulants on the result of LA tests, particularly on dPT, has not been studied extensively. Objective.-To determine whether the direct thrombin inhibitors lepirudin and argatroban and the predominantly factor Xa inhibitors enoxaparin, danaparoid, and fondaparinux could interfere with LA screening based on dPT. Design.-Each drug was added to normal and LA-positive plasmas in clinically relevant concentrations. Each sample was tested for dPT. Samples with factor Xa inhibitors were investigated before and after addition of heparinase. Mixing and confirmatory tests for LA were not performed. Results.-In the presence of lepirudin or argatroban, dPT increased notably and the dPT ratio exceeded the cutoff value even at subtherapeutic concentrations resulting in false positivity. With increasing factor Xa inhibitor concentrations, a linear increase of dPT ratios and false-positive results were also demonstrated. Although heparinase could almost completely neutralize the anti-Xa effect of all investigated factor Xa inhibitors, dPT ratio returned to the basal level only in case of enoxaparin. Conclusions.-Here we provide evidence that both the direct thrombin and indirect factor Xa inhibitors influence dPT assay for LA, causing false positivity. This should be considered when interpreting LA results during anticoagulant therapy. However, dPT seems to be a reliable test for LA screening under enoxaparin therapy after neutralization by heparinase.
    Archives of pathology & laboratory medicine 07/2013; 137(7):967-73. DOI:10.5858/arpa.2012-0236-OA · 2.88 Impact Factor
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    ABSTRACT: Dabigatran etexilate is a new oral anticoagulant for the therapy and prophylaxis of venous thromboembolism and stroke prevention in patients with atrial fibrillation. To investigate the extent of interactions of this new anticoagulant with frequently used coagulation assays, we completed a multicenter in vitro trial with Conformité Européenne(CE)-labeled dabigatran-spiked plasma samples. Lyophilized plasma samples with dabigatran concentrations ranging from 0.00 to 0.48 μg/mL were sent to the coagulation laboratories of six major Austrian hospitals for evaluation. Coagulation assays were performed under routine conditions using standard reagents and analyzer. Dabigatran led to a dose-dependent prolongation of the clotting times in coagulometric tests and influenced the majority of the parameters measured. Statistically significant interference could be observed with the prothrombin time (PT), activated partial thromboplastin time (aPTT) and PT/aPTT-based assays (extrinsic/intrinsic factors, APC-resistance test) as well as lupus anticoagulant testing. Even non-clotting tests, such as the colorimetric factor XIII activity assay and to a minor extent the amidolytic antithrombin activity assay (via factor IIa) were affected. This multicenter trial confirms and also adds to existing data, demonstrating that laboratories should expect to observe strong interferences of coagulation tests with increasing concentrations of dabigatran. This finding might become particularly important in the elderly and in patients with renal impairment as well as patients whose blood is drawn at peak levels of dabigatran.
    Clinical Chemistry and Laboratory Medicine 09/2012; 50(9):1601-5. DOI:10.1515/cclm-2011-0888 · 2.96 Impact Factor


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