What is the role of aCL antibody testing in the diagnosis of antiphospholipid syndrome (APS)?

Updated: Sep 30, 2018
  • Author: Suneel Movva, MD; Chief Editor: Herbert S Diamond, MD  more...
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Answer

aCL antibodies react primarily to membrane phospholipids, such as cardiolipin and phosphatidylserine. Of the 3 known isotypes of aCL (ie, IgG, IgM, immunoglobulin A [IgA]), IgG correlates most strongly with thrombotic events. Cardiolipin is the dominant antigen used in most serologic tests for syphilis; consequently, these patients may have a false-positive test result for syphilis.

The literature suggests that an abnormal LA finding is the laboratory test result that confers the strongest risk for thrombosis. [5, 14] LA is directed against plasma coagulation molecules. In vitro, this interaction results in the paradoxical prolongation of clotting assays, such as activated partial thromboplastin time (aPTT), kaolin clotting time, and dilute Russell viper venom time (DRVVT). The presence of LA is confirmed by mixing normal platelet-poor plasma with the patient's plasma. If a clotting factor is deficient, the addition of normal plasma corrects the prolonged clotting time. If the clotting time does not normalize during mixing studies, an inhibitor is present; the absence of a specific clotting factor inhibitor confirms that a LA is present.

Currently, there is much investigation into risk-stratifying patients based on aPL profile, aPL titers, associated autoimmune disease, and other cardiovascular risk factors. "Triple-positive" patients (LA, anti-beta-2 glycoprotein antibodies, AC antibodies) are at highest risk for thrombosis or abnormal pregnancy, and possibly for recurrence. [5] Standardized scoring systems such as the Global Antiphospholipid Syndrome Score (GAPSS) are being developed.


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