Laboratory assessment of antiphospholipid syndrome: Laboratory data

Thorough assessment of the antiphospholipid syndrome (APS) includes retesting of positive antiphospholipid antibody (aPL) tests after at least 12 weeks, and a full antiphospholipid antibody profile. To what extent this work-up is done in clinical practice is unknown.

Data on 25 116 in- and out-hospital patients tested for the presence of lupus anticoagulant (LA), the aPL which most strongly correlates with thrombosis, was extracted from the laboratory information system of the only laboratory that performs LA tests in the Capital Region, Denmark. We estimated fraction of repeated tests, tests repeated within the recommended time span, and fraction with a full aPL profile.

Out of 25 116 patients, 843 were positive for LA (3.3%), and 3948 results were inconclusive (16%). Only 51% (95% CI of the proportion: 48%-54%) (n = 431) of positive tests were repeated. The proportion of inconclusive LA test results increased from 13% (12%-15%) in 2009 to 20% (19%-22%) in 2020. Out of the positive tests repeated within the first year, only 60/353 (17%; 13%-21%) were repeated within 12-16 weeks; 177/353 (50%; 45%-55%) were re-tested within the first 12 weeks of first positive test result. The proportion of patients with a full antiphospholipid antibody profile increased from 161/1978 (8%) in 2010 to 1041/1978 (43%) in 2020.

We found several issues with the laboratory workup of APS. This indicates a need for increased awareness of comprehensive laboratory assessment of possible APS as well as a closer collaboration between the laboratory and clinicians.