Antiphospholipid antibodies in patients with antiphospholipid syndrome

Abstract

Antiphospholipid syndrome (APS) is a rare systemic autoimmune disease characterized by recurrent pregnancy morbidity or thrombosis in combination with the persistent presence of antiphospholipid antibodies (aPLs) in plasma/serum. Antiphospholipid antibodies are a heterogeneous, overlapping group of autoantibodies, of which anti-β2-glycoprotein I (aβ2GPI), anticardiolipin (aCL) antibodies and antibodies that prolong plasma clotting time in tests in vitro known as lupus anticoagulant (LAC) are included in the laboratory criteria for the diagnosis of APS. The presence of LAC antibodies in plasma is indirectly determined by measuring the length of coagulation in two tests - activated partial thromboplastin time (aPTT) and diluted Russell's viper venom time (dRVVT). The concentration of aβ2GPI and aCL (immunglobulin G (IgG) and immunoglobulin M (IgM) isotypes) in serum is directly determined by solid-phase immunoassays, either by enzyme-linked immunosorbent assay (ELISA), fluoroimmunoassay (FIA), immunochemiluminescence (CLIA) or multiplex flow immunoassay (MFIA). For patient safety, it is extremely important to control all three phases of laboratory testing, i.e. preanalytical, analytical and postanalytical phase. Specialists in laboratory medicine must be aware of interferences in all three phases of laboratory testing, in order to minimize these interferences. The aim of this review was to show the current pathophysiological aspects of APS, the importance of determining aPLs-a in plasma/serum, with an emphasis on possible interferences that should be taken into account when interpreting laboratory findings.

Keywords: anti-β2-glycoprotein I; anticardiolipin antibodies; antiphospholipid antibodies; antiphospholipid syndrome; lupus anticoagulant.

Figure 1

Manifestations of antiphospholipid syndrome.

Figure 2

Procoagulant mechanisms of antiphospholipid antibodies (21).

Figure 3

Functions of β2glycoprotein I.

Figure 4

Functions of cardiolipin.

Figure 5

Lupus anticoagulant (LAC) determination algorithm (38). The ratio is obtained by dividing the result with a low phospholipid concentration by the test with a high phospholipid concentration. dRVVT - dilute Rusell viper venom test. aPTT - activated partial thromboplastin time.