Laboratory testing for lupus anticoagulants: pre-examination variables, mixing studies, and diagnostic criteria

The latest international guidelines for the laboratory diagnosis of lupus anticoagulants (LA) date back to 1995 and are in need of revision. Various patterns of practice and interpretation by clinical laboratories have altered the intent or usage of the criteria and recommendations made at that time. Moreover, various topics in the preexamination phase of LA testing (such as the role of the clinician in test ordering, the impact of direct thrombin inhibitors or oral anticoagulant therapy, and patient biologic variation) need to be considered in future guidelines. In like fashion, examination issues relating to mixing studies will need critical review. Mixing studies have been applied to a variety of low-phospholipid LA screening assays, and no uniformity or standardization exists as to how these test results should be interpreted or if in fact they are suitable for identifying weak lupus anticoagulants.