Abstract
ABSTRACT Introduction: Thrombophilia is a thrombosis susceptibility of genetic, acquired or mixed nature. Among acquired causes, the antiphospholipid syndrome (APS) stands out as an autoimmune disease characterized by antiphospholipid antibodies, thrombotic events or recurrent gestational loss. Laboratory diagnosis is based on the detection of lupus anticoagulant (LAC), anti-β2-glycoprotein 1 and anticardiolipin; however the determination of LAC still demands uniformity. The last guideline published by the Clinical and Laboratory Standards Institute (CLSI) prioritizes the screening and confirmatory steps, to the detriment of the mixing phase. Objectives: To compare the forms of releasing the LAC and to adopt an investigation protocol in agreement with the international guidelines. Methods: Thirty-six samples with prolonged results in the screening step by the dilute Russell viper venom time (dRVVT) or activated partial thromboplastin time (APTT) were subjected to the mixing steps (1:1) and to the confirmatory steps with high concentrations of phospholipids. Results: For APTT, values whose indexes of circulating anticoagulant (ICA) were greater than 15% were considered positive. For dRVVT, the ratio between screening and confirmation was also used. Of the 36 tested samples, 14 showed correction in the mixing step, but only one resulted negative. Conclusion: ICA aided in identifying the weak antibodies that were probably diluted in the mixing step. There is no gold standard test for the diagnosis of APS, and LAC detection still requires standardization of technique and interpretation.
Highlights
Thrombophilia is a thrombosis susceptibility of genetic, acquired or mixed nature
lupus anticoagulant (LAC) investigation has limited specificity because its method is indirect and prolonged clotting times can be resulting from other non-specific inhibitors or the deficiency of factors induced by anticoagulation[2, 6]
The most commonly used tests are activated partial thromboplastin time (APTT) and dilute Russel viper venom time, since international guidelines recommend the use of two tests able to activate coagulation in distinct stages, simultaneously[7]
Summary
Thrombophilia is a thrombosis susceptibility of genetic, acquired or mixed nature. Among acquired causes, the antiphospholipid syndrome (APS) stands out as an autoimmune disease characterized by antiphospholipid antibodies, thrombotic events or recurrent gestational loss. Methods: Thirty-six samples with prolonged results in the screening step by the dilute Russell viper venom time (dRVVT) or activated partial thromboplastin time (APTT) were subjected to the mixing steps (1:1) and to the confirmatory steps with high concentrations of phospholipids. According to international classification criteria, detection of autoantibodies is necessary, among them, lupus anticoagulant (LAC), anticardiolipin antibodies (ACA), and anti-β2-glycoprotein 1 (anti-β2GP1), associated with a clinical criterion, in which are included one or more reports of confirmed arterial or venous thrombosis in small vessels, tissues or organs and/or gestational complications, characterized with at least one unexplained fetal death of a proved normal fetus, occurring from the 10th gestational week; at least one birth of a morphologically normal newborn before the 34th week due to eclampsia, preeclampsia or placental insufficiency; or at least three consecutive spontaneous abortions, with no established cause before the 10th gestational week, excluding maternal anatomical, hormonal changes or parental chromosomal alterations[1, 2]. The reagents available for APTT test vary in relation to activator, composition and concentration of
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