Antiphospholipid Syndrome Nephropathy Related Disease Diagnosed by Assessing Phosphatidylserine-dependent Antiprothrombin Antibodies

A 42-year-old Japanese woman was admitted for the evaluation of proteinuria. She had a history of four habitual abortions and valvular heart disease, including severe mitral regurgitation and moderate tricuspid re-gurgitation. A kidney biopsy showed fibrointimal thickening of interlobular arteries, fibrin thrombosis, and as-sociated focal segmental sclerosis. Although the standard test for antiphospholipid (aPL) antibodies was nega-tive, the patient was diagnosed with antiphospholipid syndrome (APS)-related disease by testing for phos-phatidylserine dependent anti-prothrombin anticardiolipin antibody, a non-criterial aPL antibody. A kidney bi-opsy may lead to a diagnosis of APS in patients with negative laboratory test findings for APS.