Cardiolipin antibodies (ACL)

Cardiolipin is a phosphorylated polysaccharide ester of fatty acids found in cell membranes. Anti-cardiolipin antibodies are seen in the antiphospholipid syndrome (APS) and in a variety of other autoimmune conditions including; vasculitis, Behçet’s syndrome, and SLE. They are included in the EULAR/ACR classification criteria for SLE. ACL Abs can be seen during the convalescent phase of acute bacterial (e.g. syphilis) and viral infections. These infection-induced antibodies are usually transient and are not associated with an increased risk of clinical complications. In general, all patients who test positive should be retested after 12 weeks to rule out transient antibodies that are usually of no clinical significance.

Persistent high titre anti-β2-glycoprotein antibodies and/or anti-cardiolipin antibodies (either IgM or IgG or both) and/or positive lupus anticoagulant constitute one of the diagnostic criteria for the antiphospholipid syndrome (APS) (arterial and venous thromboses, venous thromboembolism, thrombocytopenia and foetal loss).

Revised Sapporo/Sydney APS Diagnostic Criteria (Miyakis et al., 2006):
1. Moderate/high titre (>40 ) or above 99th centile IgG or IgM ACL/B2GP1 antibodies or Lupus Anticoagulant (LAC) positive on 2+ occasions and more than 12 weeks apart.
2. Vascular thrombosis
3. Pregnancy morbidity >10 weeks gestation or eclampsia/preeclampsia or 3+ miscarriages <10 weeks. ACL IgM/IgG and B2GP1 IgM/IgG tests are performed together using a multiplex magnetic bead based immunoassay. Screening for APS should also include lupus anticoagulant.

Diagnosis of APS
Investigation of unexplained arterial/venous thrombosis in patients <50 years Investigation of recurrent miscarriage or foetal loss

< 20 GPL/mL and < 20 MPL U/mL (reference ranges derived by manufacturer and verified in house)