The first official classification criteria for anti-phospholipid syndrome (APS) were drafted in 1998 at a workshop at the 8th International Symposium on Anti-phospholipid Antibodies in Sapporo, Japan (Sapporo criteria; Wilson et al., Arthritis & Rheumatism 1999). According to these criteria, APS can be considered proven if at least one clinical and one serological criterion are met. Clinical criteria include vascular thrombosis, which must be established according to the stipulated criteria, and pregnancy complications such as premature births, spontaneous abortions and eclampsia.
When the criteria were updated in 2004 (Miyakis criteria; Miyakis et al., Journal of Thrombosis and Haemostasis 2005) antibodies against β2 glycoprotein 1 were added. Fulfilment of the criteria now encompasses at least one of the following three parameters: antibodies against cardiolipin (ACA; IgG or IgM) or β2 glycoprotein 1 (anti-β2GP1; IgG or IgM) or a positive lupus anticoagulant (LA) test. The latter is a coagulation test. According to official recommendations the serological criteria for APS diagnosis are only fulfilled when the result is confirmed 12 weeks later in a further test. A further update of the classification criteria in 2012 (Lakos et al., Arthritis & Rheumatism 2012) included the additional recommendation that when IgG and IgM tests for ACA or anti-β2GP1 IgG are negative, IgA should be tested as well.
In serological APS diagnostics autoantibodies of several immunoglobulin classes (IgAGM) can occur simultaneously, although often only one Ig class is detected. The association of particular immunoglobulin classes (IgAGM) with particular clinical parameters is controversially discussed.
Since around 10% of the healthy normal population exhibit anti-phospholipid antibodies (APLA) in the form of ACA or LA and these antibodies can also be induced by infections or specific medications (e.g. procainamide and hydralazine), it is important to connect the serological results with clinical criteria.
ELISA is the method of choice for detection of APLA, since it is highly sensitive, simple to perform and does not require fresh plasma. EUROIMMUN offers microtiter ELISAs for quantitative determination of autoantibodies against cardiolipin, β2GP1 and phosphatidylserine. The immunoglobulin classes IgA, IgG and IgM can be investigated separately or together (IgAGM). Alternatively, lupus anticoagulant can be determined using a multi-stage procedure according to the guidelines of the International Society on Thrombosis and Haemostasis. The phospholipid-dependent coagulation tests used for this purpose have a high specificity for APS, but a low sensitivity. Moreover, since there is no gold standard, results vary depending on the test method used, making it difficult to obtain reliable serological results.
EUROIMMUN ELISAs for the detection of antibodies against cardiolipin and β2GP1 show a very high specificity in clinical studies. Sera from patients with viral hepatitis or parvovirus B19 infections and sera from healthy blood donors demonstrated only 0 to 2% positive results, while in studies using tests from other manufacturers values of between 12 and 50% were obtained. APLA can occur in cases of syphilis, which explains the somewhat high occurrence (11 to 13%) of ACA and anti-β2GP1 antibodies in these patients. The prevalence of both autoantibodies in APS (86%) and SLE (24 to 25%) corresponds to data in current literature. For ACA in particular a very high agreement with an international meta-study was found (cohort of 1000 patients, 88% of APS patients were ACA positive; Cervera R. et al., Arthritis & Rheumatism 2002).