Anticardiolipin Antibody (ACA, Cardiolipin Antibodies)

Test Description

Cardiolipin antibodies are the most common kind of antiphospholipid antibody. These antibodies are essential in the mechanism of blood coagulation. When a patient develops autoantibodies (antibodies to anticardiolipin, or ACA) against cardiolipins, he or she is at a higher risk of chronic thrombosis. There are three groups of antibodies to cardiolipin: IgG, IgM, and IgA. ACA examination is used to ascertain the cause of thrombosis, thrombocytopenia, and chronic fetal death in people with systemic lupus erythematosus.

Normal Values

IgG Cardiolipin Antibody

  • Negative: <10 GPL
  • Equivocal: 10–40 GPL
  • High Positive: >40 GPL

IgM Cardiolipin Antibody

  • Negative: <12 MPL
  • Equivocal: 12–40 MPL
  • High Positive: >40 MPL

IgA Cardiolipin Antibody

  • Negative: <12 APL
  • Equivocal: 12–40 APL
  • High Positive: >40 APL


Groups APL, GPL, and MPL belong to arbitrary attribute groups. The abbreviation APL denotes the outcome as IgA isotype, GPL denotes the outcome as IgG isotype, and MPL denotes the outcome as IgM isotype. The letters “PL” denote the antigen specificities for phospholipids. The antiphospholipid syndrome (APS) is described by positive and highly positive tests for IgG and IgM phospholipid (cardiolipin) antibodies (> 40 GPL and/or > 40 MPL). Patients with APS that have clinical signs show lower rates of IgG and IgM phospholipid (cardiolipin) antibodies and IgA isotype antibodies, but the results are not considered diagnostic. To meet the laboratory diagnostic criteria for APS, phospholipid (cardiolipin) antibodies must be detected on at least two occasions, at least 12 weeks apart.

Possible Meanings of Abnormal Values


  • Antiphospholipid syndrome
  • Idiopathic thrombocytopenic purpura
  • Psoriatic arthritis
  • Rheumatoid arthritis
  • Sjögren’s syndrome
  • Systemic lupus erythematosus

Contributing Factors to Abnormal Values

  • Current or past infection with syphilis may cause a false-positive ACA result.
  • Drugs that may cause a positive ACA: anticonvulsants, antibiotics, hydralazine, oral contraceptives, phenothiazines, procainamide.



  • Explain to the patient the purpose of the test and the need for a blood sample to be drawn.
  • No fasting is required before the test.


  • A 7-mL blood sample is drawn in a gold-top (serum separator) collection tube.
  • Gloves are worn throughout the procedure.


  • Apply pressure at venipuncture site. Apply dressing, periodically assessing for continued bleeding.
  • Label the specimen and transport it to the laboratory.
  • Report abnormal findings to the primary care provider.


The phospholipid (cardiolipin) immunoassay does not distinguish between autoantibodies and antibodies formed in response to infectious agents or after thrombosis as an epiphenomenon. For this reason, a single positive test result is insufficient for the diagnosis of antiphospholipid syndrome (APS) based on established serologic criteria.

Comparative analysis and interlaboratory attribute evaluations reveal that effects from phospholipid antibody tests can be highly unreliable, and results from various commercial immunoassays can yield substantially different results.


  • McGraw Hill Manual of Laboratory and Diagnostic Tests

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