Cardiolipin antibodies (ACL) (Anti-Phospholipid Antibodies)
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.
Persistently positive moderate or high titre anti-β2-glycoprotein antibodies and/or anti-cardiolipin antibodies (either IgM or IgG or both) and/or positive lupus anticoagulant measured on two occasions at least 12 weeks apart, constitute one of the diagnostic criteria for the antiphospholipid syndrome (APS) (arterial and venous thromboses, venous thromboembolism, thrombocytopenia and foetal loss).
See 2023 ACR/EULAR antiphospholipid syndrome classification criteria. Barbhaiya M, et al. Ann Rheum Dis 2023;82:1258–1270. doi:10.1136/ard-2023-224609.
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 (LA) test.
See Lupus anticoagulant (LA) screen / Special Coagulation Services.
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)
Please note, this test is part of the Anti-Phospholipd Antibodies screen
This test is currently unaccredited due to a relocation of the analyser (no changes to assay used)
This test is not currently accredited
Record last updated
February 17, 2026
Sample Container
5ml RST Vacutainers (Rust top)
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UKAS accredited medical laboratory/medical diagnostic service:
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Our laboratories are accredited by the UK Accreditation Service (UKAS) against the international standard ISO15189:2022. UKAS is the accreditation body for the UK that assesses medical laboratories.
Find out more about our accreditations on the UKAS website.
UKAS website