New Aspects of Laboratory Diagnostics of Antiphospholipid Syndrome

Antiphospholipid syndrome (APS) is a clinical and laboratory symptom complex characterized by recurrent thrombosis, obstetric pathology and the synthesis of antiphospholipid antibodies (aPL). The 2023 ACR/EULAR APS classification criteria differ from the previous ones (Sapporo, 2006) by a weighted assessment in points and the allocation of a mandatory “entry” criterion, which contains at least one clinical sign plus a positive result of the aPL test, including detection of lupus anticoagulant (LAC) or moderate (40-79 U) or high (≥80 U) levels of IgG/IgM antibodies to cardiolipin (aCL) or IgG/IgM antibodies to β2-glycoprotein I (aβ2-GP I) in blood within 3 years after identifying the clinical criterion. The greatest significance for diagnosing APS and predicting a high risk of thrombotic complications is the persistent detection of LAC and highly positive levels of IgG aCL and/or IgG aβ2-GP I, the least important is a single identification of LAC and persistent detection of moderate/high positive levels of IgM aCL and/or IgM aβ2 -GP I. The ACR/EULAR 2023 classification criteria for APS have greater diagnostic specificity (99% vs 86%), but lower diagnostic sensitivity (84% vs 99%) compared to the previous ones (Sapporo, 2006).