Lupus anticoagulant testing: effect of the platelet count on the activated partial thromboplastin time.

The activated partial thromboplastin time (APTT) is often used as a test to diagnose patients with lupus anticoagulants. It is recommended that platelet-poor plasma be used in the APTT test. In this study the effects of residual platelet contamination on lupus anticoagulant and antiphospholipid antibody testing are described. In fresh samples the residual platelet contamination has no significant effect whereas in frozen samples the effect of residual platelet contamination can have a significant effect on the APTT testing.