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The combination of lupus anticoagulant sensitive and insensitive aPTT reagent together with dRVVT screening reagent for the exclusion of the presence of lupus anticoagulant

The heterogeneity of lupus anticoagulants (LAs) makes it impossible to use only one coagulation assay for the laboratory detection of LAs implicating the need to perform a combination of at least two different assays. There is consensus regarding the general principles of LA testing according to the guidelines proposed by the SSC on LA and phospholipid-dependent antibodies of the ISTH but no agreement on the optimal methodology with any of the coagulation assays and on the nature and concentration of phospholipids. The aim of this study was to apply two different commercial aPTT reagents with different LA sensitivity together with dRVVT screening reagent as the first set of assays to rule out the presence of LA. For this purpose, we have analyzed plasma samples from 100 patients with request for the determination of LA which had previously been tested with our routine procedure for the laboratory detection of LA. Among tested samples, 70 were LA negative (20 on OAT, INR:1.29-3.57) and 30 were LA positive (5 on OAT, INR:1.35-6.80). aPTT was performed by using Actin FS (Dade Behring) as LA insensitive reagent and Dapttin (Technoclone) as LA sensitive reagent together with LA1 (Dade Behring) as dRVVT screening reagent. Whenever needed, the assays were repeated after mixing the samples with normal plasma in a ratio 1:1. All assays were performed simultaneously on BCT analyzer (Dade Behring). Finally, the results were expressed as aPTT LA ratio between clotting times obtained with Dapttin and Actin FS. Significant difference in aPTT LA ratio (p<0.001) was obtained in the group of LA positive samples (mean 1.89, range 1.06-3.30) as compared to the group of LA negative samples (mean 1.29, range 0.98-1.48). There was no difference in aPTT LA ratios (p=0.03) between patients on OAT (mean 1.25, range 1.09-1.48) and patients not receiving OAT (mean 1.31, range 0.98-1.44) in the group of LA negative patients. The majority of LA positive samples 24/30 (80%) gave aPTT LA ratios greater than 1.50 (mean 2.05, range 1.50-3.30), including all 5 samples on OAT. In the remaining 6 LA positive samples with dRVVT screen/confirm positive test only, aPTT LA ratios ranged between 1.06 and 1.43 (mean 1.29). The combination of assays in our study is a rapid and simple method to rule out the presence of LA even in patients on OAT and enables even small laboratories performing basic hemostatic profiles to perform reliable screening for the presence of LA.

lupus anticoagulant; aPTT reagents

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