Use of a modified activated partial thromboplastin time to detect lupus anticoagulants

Laboratory evidence for the presence of lupus anticoagulants (LAs) is sought when patients experience thrombotic events or when coagulation assays are abnormal. Although a number of tests for LAs have been proposed, none detect all LAs, and laboratories may be confronted with the need to perform more than one test to confirm a suspected LA. Recently, a modification of the aPTT, performed by varying the initial time of incubation of the aPTT reagent with the patient's plasma, was reported to detect LAs. The difference in clotting times when plasma is subjected to a 1- or 10- minute incubation (called here the "Delta one minus ten" or DOT) using a particular micronized silica-based aPTT reagent was shown to provide good discrimination between normal and LA plasmas. Because of the low cost of this test and its relative ease of performance, we attempted to replicate the results of this test using previously characterized LA plasmas. The DOT of 23 normal plasmas was 5.1 +/- 2.1 seconds, with a range of 0.5 - 9.3 seconds. The DOT of 20 of 34 LA samples tested (59%) was > 11 seconds. The DOT was abnormal in 8 of 22 (36%) samples diagnosed with a dilute Russell's viper venom time. It was abnormal in 12 of 12 patients diagnosed by other criteria, prior to the use of the dilute Russell's viper venom time. The DOT performed with a kaolin or ellagic acid-based aPTT reagent failed to discriminate normal from LA plasma. We conclude that the DOT performed with a specific silica-based reagent is an apparently simple and moderately sensitive test for detecting the lupus anticoagulant that deserves further evaluation.