MIXCON-LA: A Precise, Sensitive and Specific aPTT-Based Assay for Detection of Lupus Anticoagulant

Abstract

Lupus anticoagulants (LA) are associated with an increased risk of thrombosis and laboratory detection is of major importance. Multiple tests are available for screening and confirmation, but they differ in sensitivity and specificity, frequently lacking the ability to discriminate between the presence of LA, heparin, and oral anticoagulants. Based on the test-principle of the Lupus Ratio-test, an automated, sensitive APTT-based assay, using mixtures of a lupussensitive and a lupusinsensitive APTT-reagent with normal plasma for detection of lupus anticoagulants was developed. Ninety-nine healthy volunteers, ten patients treated with unfractionated heparin intravenously, 19 patients taking stable oral anticoagulation, five patients with hemophilia A, and 15 patients with antiphospholipid-antibody-syndrome (APS) were investigated. In all patients, two APTTs were performed, one with each reagent, on 1:1 mixtures of test plasma and normal plasma (MIXCON-LA assay). The ratio between the two clotting times was divided by the corresponding ratio for the normal plasma. This final lupus ratio (LR) was used for evaluation. The within-series imprecision and the between-series imprecision were excellent with coefficients of variation between 1.5% and 1.9%. The mean +/- 2 SD of the LR of the 99 healthy volunteers was used as reference range (LR: 0.95-1.07). All patients treated either with heparin or oral anticoagulants remained negative in the MLXCON-LA assay (specificity, 100%), while one of five patients with hemophilia A, in whom a factor VIII-inhibitor developed, showed a false-positive result. In 13 of 15 patients with APS, an increased ratio was observed (sensitivity, 87%). This assay system allows precise, specific, and sensitive detection of lupus anticoagulants.

IgG/IgM antiphospholipid antibodies present in the classification criteria for the antiphospholipid syndrome: a critical review of their association with thrombosis

“…The main reasons for exclusion included: no correlation of serologic results with thrombosis; measurement of only IgG or only IgM antibodies; no discrimination between IgG and IgM antibodies; presentation of combined antibody results; only LA/non‐criteria antibodies being measured; and the inclusion of overlapping patient populations. Thus, 177 studies were included in this systematic review . Those studies were grouped according to their analysis method: those containing ORs for thrombosis or allowing their calculation, and those for which, owing to a lack of information, only the percentage of positive patients in the thrombotic population can be shown.…”

Screening for lupus anticoagulants in patients treated with vitamin K antagonists

“…For both aPTT assays, a calcium chloride solution (0.025 m ) containing polybrene was used to avoid false‐positive test results in plasma samples containing therapeutic heparin doses. These assays have previously been described in detail .…”

Immune Response to FVIII in Hemophilia A: An Overview of Risk Factors

“…This issue can largely be avoided by using high phospholipids containing APTT reagents for FVIII inhibitor assays, which combine both functional, and ELISA assays. More sensitive assays are now available to detect anti-FVIII antibodies without interference from LA [64,65].…”