Laboratory testing for lupus anticoagulants
Abstract The diagnosis of LA requires special attention to specimen processing and careful determination of a reference interval for the screening procedures. A sensitive APTT reagent should be used as the routine screen with appropriate secondary screening procedures available for the difficult patient (e.g., KCT and dRVVT). Appropriate attention to the ratio of patient to normal plasma in mixing studies is imperative. The ratio of four parts patient to one part normal is recommended. In some instances, confirmatory tests utilizing either the PNP or other test systems may be ambiguous. In these cases it is necessary to perform factor assays for a definitive diagnosis. There is a need for reference plasmas and a common means of expressing LA titers.