Audit of laboratory investigation of antiphospholipid syndrome

Abstract

Antiphospholipid syndrome (APS) diagnosis has serious consequences for the patients, due to decisions being made on anticoagulation. Despite the improved understanding of the true nature of aPLs the interpretation of APS laboratory investigation test results is still difficult and fraught with pitfalls, which may occasionally lead to underdiagnosis and frequent to overdiagnosis of the syndrome. We audited the laboratory investigation of APS and analyzed the prevalence of different aPLs (antiphospholipid antibodies) positivity profiles. A patient's sample was considered positive if anticardiolipin antibodies (aCL), lupus anticoagulant (LA) and anti-β2-GPI were tested and one of them was abnormal. Both a CL and LAwere tested in 98.1% of samples (1088/1109) and 190 of them (17.13%) were considered to be a PLs positive, aCL and LA positivity coincided in only 34.1% of the positive samples. Only 57 of the 164 aCL-positive samples were found to be anti-β2-GPI IgG positive (28%) but there was a better concordance in positivity with the medium-high a CL-positive group (60%). The anti-β2-GPI was an isolated abnormality in only 2 of the aPLs-positive samples. Of the aPLs-positive samples 13.5% were detected as solely a CL IgG-positive with a titre of less than 20 anticardiolipin units and 14.21% as solely aCL IgM-positive. Those two groups were characterized as equivocal positive samples. Both aCL and LA are required to identify all abnormal patients. Less than 30% of the aCL-positive samples were anti-β2-GPI IgG positive. An important proportion of patient's samples results (27%) needed careful interpretation due to equivocal aCL results.