No abstract

The data confirmed the lack of standardisation in methodology employed in different centres. Updated guidelines and standardisation of platelet function assessment are required to facilitate comparability between centres.

SummaryThe identification of the presence of antiphospholipid in plasma is recognised to be of diagnostic and prognostic importance in subjects with thrombotic disease, recurrent miscarriage or collagen vascular disorders. A number of coagulation assays are currently employed for the detection of lupus anticoagulant (LA), many of which are influenced by reagent dependent and methodological variables.In the present study lyophilised plasma samples from three subjects with “strong”, “weak” and “absent” LA were tested in 220 centres. The most commonly used tests for LA were Activated Partial Thromboplastin Time (APTT), Dilute Russell Viper Venom Time (DRVVT) and Kaolin Clotting Time (KCT). Median DRVVT ratios were 1.75, 1.17 and 1.10 for the three samples. The presence of a strong LA was not detected by 4% of laboratories. The correct diagnosis was made by 94% of users of DRVVT and 85% of users of KCT. A weak LA was not detected by over half of centres. Correction was observed on addition of plasma and also in platelet neutralisation. The correct diagnosis was made by 37% of users of DRVVT and 27% of users of KCT. Lupus Anticoagulant was falsely considered to be present in a Factor IX deficient plasma by approximately one quarter of laboratories. Amongst users of DRVVT and KCT absence of LA in this sample was correctly reported by 73% and 69% of centres respectively.The accuracy of testing for LA in the present study is suboptimal and this is likely to have important clinical consequences. There is clearly a need for greater conformity in the selection and performance of LA tests to facilitate accurate diagnosis of this important group of disorders.

Global hemostasis devices are currently being employed in operating rooms to assess the bleeding risk and outcomes for patients undergoing surgery. Two devices currently available are the TEG (Thromboelastograph; Haemoscope Corp., Niles, IL) and the ROTEM (Rotation Thromboelastometer; Pentapharm GmbH, Munich, Germany). Both measure the speed of clot formation, the strength of the clot when formed, and clot fibrinolysis kinetics. The two devices use different parameters so no cross comparisons of results can be made. The devices are usually operated by a member of the operating team and not a laboratory scientist; thus their testing and performance is generally not laboratory controlled, despite quality control being required to ensure reliable results. The UK National External Quality Assessment Scheme (NEQAS) for Blood Coagulation has undertaken a series of exercises evaluating the provision of External Quality Assessment (EQA) material for these devices. A series of four studies have taken place using lyophilized plasmas as the test material. Up to 18 TEG users and 10 ROTEM users have been involved in testing two samples per study, for a total of eight samples tested. The samples were normal plasmas, factor VIII or XI deficient samples, or normal plasmas spiked with heparin. The precision of the tests varied greatly for both devices, with coefficients of variances ranging from 7.1 to 39.9% for TEG and 7.0 to 83.6% for ROTEM. Some centers returned results that were sufficiently different from those obtained by other participants to predict alterations in patient management decisions. Our data indicate that regular EQA/proficiency testing is needed for these devices.

Summary. Laboratory screening for lupus anticoagulant (LA) has been shown to be suboptimal in several studies. Guidelines have recently been published by an expert group for the British Committee for Standards in Haematology, in an attempt to standardize and improve screening procedures. The value of using screening tests conforming with these guidelines was investigated in a United Kingdom National External Quality Assessment Scheme (UK NEQAS) proficiency testing exercise. The correct diagnosis was achieved by 97% of laboratories for a LA-negative sample. However, 18AE3% of centres reported a false-negative result for a sample from a LA-positive subject. A significantly higher proportion of centres that used methods conforming with the published guidelines achieved the correct diagnosis for this sample (P < 0AE002, chi-square test). A wide variety of screening tests were used by laboratories in this study. Within-method agreement could be improved by the use of a common normal pooled plasma to determine ratios. However, between-method agreement was not improved by this procedure. We conclude that adoption of methods compliant with national guidelines may improve the diagnosis of LA. There is a need, however, for reference and standardization materials to ensure further improvement in the accuracy of LA methods.