hematology and oncology
Antiphospholipid Syndrome (APS)
Diagnosis of Antiphospholipid Syndrome
Laboratory testing, beginning with partial thromboplastin time (PTT) and the dilute Russell viper venom time (DRVVT) In patients with clinical events (thrombosis or pregnancy loss) that suggest APS, laboratory testing should be done to confirm the diagnosis. In the presence of antiphospholipid antibodies, the PTT is prolonged and does not correct with 1:1 or 4:1 mixing with normal plasma. Correction of the PTT after adding excess purified phospholipids is consistent with the presence of an antiphospholipid antibody. The dilute Russell viper venom time (DRVVT) is another assay to detect the lupus inhibitor. It is more sensitive than the PTT to the presence of antiphospholipid antibodies. The venom causes coagulation by activatingfactor X. The presence of lupus anticoagulant prolongs the clotting process. Normal plasma has no effect on the clotting time, but addition of excess phospholipid reverses the prolongation. Immunoassays for IgG and IgM antibodies against cardiolipin and beta-2 glycoprotein 1 are also done. It is important to do both immunoassays and coagulation assays when diagnosing APS because some patients will only have positive results for one test. To confirm the diagnosis, the positive tests should be repeated 12 weeks after initial testing to confirm abnormal results. 