Clinical audit of antiphospholipid antibody testing in tertiary practice: towards improved relevance in thrombophilia investigations.

Background: The antiphospholipid syndrome (APS) is an autoimmune condition characterised by vascular thromboses and/or pregnancy morbidity. Diagnosis of APS typically requires laboratory evidence of antiphospholipid antibodies (aPL). Depending on their clinical presentation, affected individuals might be seen by a variety of clinical specialities.

Aim: To evaluate clinical ordering patterns for aPL/APS at a tertiary level public facility.

Methods: We performed an audit of internal clinical requests for aPL tests at our institution for a 6-month period.

Results: We identified a wide variety of clinical ordering background for aPL, of predominantly obstetric (72/268; 26.9%) or thrombophilic (78/268; 29.1%) patients. Only 11/268 samples (4.1%) were positive for lupus anticoagulant (LA) and 14/268 (5.2%) were positive for anticardiolipin antibody (aCL). The percentage of aCL positivity in the LA-positive group was 46% (5/11). None of the 72 obstetric patients tested was identified to have aPL. Of the 11 LA-positive patients, the reasons identified for testing comprised: prolonged Activated Partial Thromboplastin Time (assay) (n= 3), thrombosis (n= 3), APS (n= 2), systemic lupus erythematosus (n= 2), vasculitis (n= 1).

Conclusion: We determined a wide variety of clinical ordering background for aPL at a tertiary level institution, with an overall low rate (<10%) of aPL positivity among a hospital population of predominantly obstetric or thrombophilic patients. That no positive obstetric aPL cases were identified suggests local clinical ordering guidelines may need review, as also potentially practised at other institutions. We also observed a moderate rate (46%) of coincidence of aCL and LA, in agreement with guidelines indicating that multiple tests are required to identify APS.