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Abstract
The diagnosis of lupus anticoagulant (IL) according to the classical algorithm (ISTH) is prolongation of some of the screening tests (Russel or APTT sensitive), the non-correction of the mixing test and the shortening of the elongated test times in presence of high concentration of phospholipids. The guide of the British Hematology Society (BSH) suggests that, in the absence of other coagulation abnormalities, if a sample is positive screen and confirmatory test although the tests of mixtures are negative, should be considered positive for IL. The CLSI guide suggests performing the tests in the following order screenconfirm- mix; recommends that the mixing test be carried out only when the first two do not have a clear result and if other abnormalities are suspected. The objective is to compare the final diagnosis for lupus anticoagulant (IL) applying the BSH/CLSI guidelines vs the classical algorithm (ISTH). Population: 196 samples of positive lupus inhibitor by BSH and CLSI referred to our laboratory between March 2015 and May 2017. Methods: a sensitive APTT assay containing microtonized silica was used as activator (SCT screen and confirm) and the diluted and concentrated Russell viper venom test (VVRT screen and confirm). Results: analysis with ISTH algorithm: samples with positive screening 33/196 by APTT and 28/196 by Russell corrected the mixing assay, no confirmatory test was performed and they were considered negative for lupus inhibitor. Analysis with the BCH / CLSI algorithm: positive confirmatory test, correction in the assay of mixtures and absence of another alteration of coagulation in 33/196 via the APTT and 28/196 with the Russell test and were considered positive for IL, positive confirmatory test and no correction in the mixture test 123/196 by the APTT and 96/196 by the Russell. There are 61/196 that would be positive for the BSH / CLSI Guidelines and negative for ISTH with a normalized Russell ratio 1.27 (range: 1.22-1.32) and normalize ratio SCT 1.36 (range: 1.32-1.41). Of the 61 patients, 14 had DVT, 17 obstetric pathology, 12 had autoimmune diseases, 3 presented cerebrovascular accidents and only 15 were laboratory findings. Conclusion: there are patients who develop an antibody that, in vitro, has a weak effect that disappears by dilution effect when mixed with normal plasma, which causes it to be interpreted according to the traditional algorithm as negative. However, these antibodies are persistent, 34/61 (55.7%) presented clinical manifestations that determined the diagnosis of anti-phospholipid syndrome.
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