Standardization of Lupus Anticoagulant : The Lupus Anticoagulant Sensitivity Index (LASI)

Results for lupus anticoagulant (LA) are expressed as ratio of patient-to-normal clotting times (LA-ratio) according to the equation LA-ratio=(PatientClotting time/NormalClotting time). However, numerical results vary according to the method used for testing, thus making difficult the between-method and between-laboratory comparison of results. The hypothesis that the standardization model currently employed for the international normalized ratio for patients on warfarin is valid also for LA standardization has been taken into consideration. The model calls for the determination of a LA-sensitivity index (LASI) for each commercial method for LA detection against a common standard method. The LASI is then used to convert the LA-ratio into a scale called standardized LA-ratio (SLA-ratio) according to the equation SLA-ratio=(LA-ratio)LASI. The model proved effective in minimizing the between-method variability of results for LA detection. If implemented it could be a valuable tool to improve the comparability of results obtained in different laboratories, to quantify the LA potency and thus pave the way to the organization of collaborative clinical trials aimed at assessing whether the potency of LA is a risk factor for clinical events.