Two types of tests are used in diagnosis of the antiphospholipid syndrome:

• lupus anticoagulant (LA) tests, in which the capacity of a plasma is tested to inhibit in vitro the clot formation by the so-called LA antibodies: Dilute Russell viper venom time, kaolin clotting time, tissue thromboplastin inhibition test.
• specific ELISA to detect antiphospholipid antibodies.

LA antibodies mainly affect coagulation reactions via the recognition of lipid-bound prothrombin complexes and may be therefore better named anti-prothrombin antibodies instead of LA antibodies (151). Up to now their clinical significance is not clarified (153).
To a lower extent LA activity in the plasma of patients with APS can reflect the presence of autoantibodies to bGP-1. Whether LA activity tests and specific ELISA measure similar phenomena is not clarified, since the binding specificity of antiphospholipid antibodies is perhaps not suited to predict the biological effects of these antibodies (154). Reagents commercially available for the LA tests vary in phospholipid origin and concentration (155), therefore ELISA using specific and well defined antigens should be preferred.
Since bGP-1 is up to now the most common and best characterized antigenetic target for antiphospholipid antibodies (156-159), numerous ELISA have been developed to detect antibodies against bGP-1 as a marker for the antiphospholipid syndrome (160-169). At present new ELISA are available recognizing IgA-, IgG- and IgM-antibodies directed to phospholipids (e.g. cardiolipin, phosphatidyl-serine, phosphatidyl-inositol, etc.) alone as well as directed to complexes between these phospholipids and bGP-1 or prothrombin. The use of such specific ELISA are important for the standardization and should lead not only to a better comparability of the results but also to a better understanding of the pathogenesis as well as to an improvement of the risk assessment.
For example, it could already be shown that antibodies reactive with phosphatidyl-ethanolamine are very closely associated with early recurrent pregnancy loss (170). Moreover, IgG-anticardiolipin antibodies and, to a lesser extent IgM-isotypes, are reported to be the highest risk factors for the clinical manifestations of APS. Also evidence that IgA antibodies may be important continues to accumulate (171, 172). IgA may be the most common isotype in black patients with SLE and primary APS (173, 174).
False-positive results obtained by standard syphilis tests such as venereal disease research laboratory (VDRL) and Wasserman tests, may be caused by antiphospholipid antibodies.

Since antiphospholipid/antiprothrombin antibodies may consume the substrate for the coagulation factors they can lead especially to a prolongation of the activated partial thromboplastin time (aPTT). Therefore antiphospholipid/antiprothrombin antibodies should be taken into consideration in case of an unexplainable prolongation of aPTT.

Anti-phospholipid Antibodies - Sample
Serum
Specimen stable at 2-8°C for 1 week.

Anti-phospholipid Antibodies - Methods

Anti-phospholipid Antibodies - ELISA
See Antinuclear Antibodies – ELISA.

Anti-phospholipid Antibodies – Indirect immunofluorescence assay
See Antinuclear Antibodies – Indirect immunofluorescence assay.

Anti-phospholipid Antibodies - Radioimmunoassay
See Antinuclear Antibodies – Radioimmunoassay