Evaluation of a new silica clotting time in the diagnosis of lupus anticoagulants

Abstract

Introduction A new commercial silica clotting time (SCT), the HemosIL™ SCT assay (Instrumentation Laboratory, Milan, Italy) was evaluated in the laboratory diagnosis of lupus anticoagulants (LAC). This integrated test system for screening and confirmation was compared with the frequently used aPTT-based PTT-LA and Staclot-LA (Diagnostica Stago, Asnières, France) in a patient population investigated for LAC and in a subpopulation who met the clinical criteria for antiphospholipid syndrome (APS). Materials and methods 201 samples were analysed with the HemosIL™ SCT assay. Own reference values were calculated. Results are expressed as measured clotting times in seconds or as normalised ratios. Results SCT screen and PTT-LA had a sensitivity of, 61.1% and 63.8%, respectively. Normalising the results gained sensitivity up to 72.2% and 90%, respectively. The confirmation SCT and the Staclot-LA had a sensitivity of 30.6% and 63.9% with a specificity of 86.7% and 100%, respectively. Sensitivity of SCT for detecting LAC in clinical criteria positive patients was lower compared to aPTT and dRVVT (45.8% versus 66.7% and 65%). Combination of SCT/dRVVT and aPTT/dRVVT gave a sensitivity of 51.2% and 63.6%, with a specificity of 50.0% and 52.3%, respectively. Conclusions In comparison with PTT-LA as screening test, the SCT screen shows an acceptable sensitivity. However, the HemosIL™ SCT assay including the confirmation step, has a much lower sensitivity in the diagnosis of LAC in comparison with the Staclot-LA test. Combining the HemosIL™ SCT assay with dRVVT results in a better sensitivity, although lower than the combined aPTT/dRVVT based method as usually performed in our lab.