Trials and tribulations in lupus anticoagulant testing.

This issue of Clinical Chemistry and Laboratory Medicine includes a report by Pradella and colleagues regarding a cooperative multicentre study to define the upper limits of normal for several tests used in the diagnostic assessment of lupus anticoagulant (LA) [1] . In total, 200 normal samples were assessed, comprising 40 from each of five centres, for a total of six functional LA assays. Each centre used the same tests, dilute Russell viper venom time (dRVVT) (screen and confirm), and silica clotting time (SCT), the same reagents and the same type of instrument from a single manufacturer. This is a notable report for several reasons, apart an interesting observational exercise around the concepts of standardisation (use of common products, procedures, processes, and practices) and harmonisation (the process whereby different analytic systems are determined to provide clinically similar results) of LA testing. The study explores an interesting approach to a common laboratory problem – undertaking studies with sufficient numbers of normal individuals to establish a critical cut-off value that will help define patients ‘ with ’ or ‘ without ’ LA. This is an important component of the laboratory evaluation of the antiphospholipid syndrome (APS) [2, 3] , in turn having significant implications for patient management [2 – 4] . In brief, patients identified clinically to have APS, as diagnostically aided using laboratory assessment by LA, can be subjected to long-term anticoagulant therapy, which has significant implications for both lifestyle changes as well as bleeding and thrombosis risk. In essence, an incorrect diagnosis will have significant clinical and social implications; a false-positive diagnosis of APS may subject a patient to unnecessarily longterm anticoagulant therapy with risk of bleeding, whereas a false-negative diagnosis may mean the patient is not appropriately anti-coagulated and therefore at future risk of thrombosis. Current LA guidelines [5] suggest that laboratories use ‘ at least 40 adult healthy donors ’ and take ‘ the cut-off as the value above the 99th percentile of the distribution ’ . This has caused some contention in the field, given that a statistically valid 99th percentile evaluation of a nonGaussian distributed normal population would require a minimum of nearly 400 samples [6] . Pradella and colleagues [1] comparatively evaluated the data obtained in each assay, as well as assay ratios, in each center, as well as the composite of all study data. Notably, when assay data was expressed in seconds, some test results showed a normal Gaussian distribution, whereas others did not, and there were also some statistically significant differences in results obtained between centers. In contrast, when results were expressed as normalised ratios, the test results were normally distributed and there were no longer any statistically significant differences in data between centres. Thus, better agreement between centres, and in essence standardisation and harmonisation, was obtained when data was interpreted in terms of normalised ratios. In LA testing, there is actually very limited consensus in terms of inter-laboratory processes. Thus, different laboratories use different test procedures [e.g., based on dRVVT, SCT, activated partial thromboplastin time (APTT), kaolin clotting time (KCT) and/or other tests], different test panels (e.g., APTT ± dRVVT ± KCT ± SCT, etc.), different test app roaches [testing of neat plasma vs. testing of mixed plasma (i.e., patient plus normal), sometimes using different test plasma:normal plasma mixtures], different ways of interpreting test results (e.g., test ratios [division], test differences [subtraction], percent corrections, Rosner Index), and different cut-off values [6 – 9] . Of interest, Pradella and colleagues [1] determined a cut-off value of 1.22 for the dRVVT normalised ratio. This value is actually very close to that value ‘ nominally ’ indicated on many dRVVT product information sheets, as well as generally used by laboratories. For example, Figure 1 A shows data from the Australasian College of Pathologists of Australasia (RCPA) Haematology Quality Assurance Program (QAP) [10] . Most laboratories report a negative LA