Activated partial thromboplastin time reagent sensitivity to the presence of the lupus anticoagulant.

The lupus anticoagulant (LA) is an acquired abnormality that is associated with a prolonged activated partial thromboplastin time (aPTT). It is one of the most frequent coagulation abnormalities seen in the routine clinical laboratory. The sensitivity of various commercial aPTT reagents varies in their ability to detect the LA. We undertook this evaluation by using a single coagulation instrument to determine the sensitivity of five different commercial aPTT reagents to the presence of the LA. We evaluated 23 patients with known LA using five different reagents, two of which were marketed as having enhanced LA sensitivity. All samples and testing were performed under the same conditions in a timely manner. Based on these data, essentially all of the commercial reagents that were tested could detect patients with known LA by at least minimally prolonging the aPTT. Some reagents were slightly better than others in their ability to detect the LA. For most hospitals, the detection of the LA is not the highest priority for the use of the aPTT assay. In most cases, heparin anticoagulation monitoring is the most common use of the aPTT assay. Since all five reagents are sensitive to the LA, then the best overall reagent will be the one with the best sensitivity to the most important need for the laboratory (usually heparin monitoring). Therefore, a reagent should be chosen based on the primary monitoring requirements of the aPTT assay, and greater than 90% of the patients with the LA will be detected.