COMPARISON OF A STANDARDIZED PROCEDURE WITH CURRENT LABORATORY PRACTICES FOR THE DETECTION OF LUPUS ANTICOAGULANT IN FRANCE

A multicenter study involving 13 laboratories was designed to compare a common procedure for screening lupus anticoagulants (LA) to the diff erent practices currently in use in these laboratories. The common pro cedure combined 3 phospholipid-dependent assays, including mixing stud ies and a phospholipid neutralizing test. Due to the heterogeneity of LA expression, an abnormal result in at least one of the tests was suf ficient to classify a sample as positive for LA. Consecutive samples r eferred for LA diagnosis were evaluated in parallel by each participan t and the data found using the common procedure were analyzed independ ently according to mutually agreed cut-offs and criteria for sample cl assification. Within a period of 3 months, 535 samples were included, of which 147 were judged LA positive, 29 undetermined and 359 negative by the respective laboratories using their current practice. When usi ng the common procedure, 149 plasmas were said to be positive, 38 unde termined and 348 negative. Absolute concordance occurred for 81% of th e specimen population and absolute discordance (positive versus negati ve) for 7%. The level of agreement between the common procedure and th e current practices, assessed by kappa indexes, indicated noticeable v ariations in the rates of detection from laboratory to laboratory. Amo ng the different tests used in the common procedure, regular APTT was the least sensitive (about 50% detection) but none of the other tests alone recognized more than 73% of specimens from the LA positive popul ation. This yield increased to about 90% with any combination of 2 sen sitive tests. The common procedure should not be considered as a metho dological gold standard but as an acceptable basis for the collaborati ve works required for the improvement and standardization of laborator y practices for screening LA.