An international consensus statement on classification criteria for definite APS was published in 1999. A patient with APS must meet at least one of the two clinical criteria (vascular thrombosis or pregnancy complications) and at least one of the two laboratory criteria (aCL and/or LA). Although these criteria have been shown to be specific and sensitive for the classification of primary and secondary APS, the absence of "major" or "essential" features in the presence of "minor" features should not discourage the clinician from making the diagnosis when other causes of such features have been ruled out, since other well-recognized features of APS such as thrombocytopenia, hemolytic anemia, transient ischemic attacks, transverse myelitis, livedo reticularis, valvular heart disease, demyeli-nating syndromes, chorea, and migraine were not thought to have as strong an association as the final criteria and were excluded as classification criteria. These criteria have been revised in 2006 to include anti-b2GPI as a laboratory criterion for APS, and laboratories around the world are being encouraged to standardize their methodology for the detection of these antibodies (Table 4.1).
Table 4.1. 2006 preliminary criteria for the classification of definite antiphospholipid syndrome.
Vascular thrombosis: > one arterial, venous, or small vessel thrombosis in any tissue or organ, confirmed by imaging or histopathology in the absence of significant evidence of inflammation in the vessel wall Pregnancy morbidity
>One unexplained death of a morphologically normal fetus at or beyond the tenth week of gestation
>One premature births of a morphologically normal neonate at or beyond the 34th week of gestation, due to severe preeclampsia, eclampsia, or placental insufficiency
>Three unexplained consecutive spontaneous abortions before the tenth week of gestation (maternal anatomic or hormonal abnormalities and chromosomal causes excluded)
Medium or high titers of IgG and/or IgM aCL measured by a standardized ELISA for b2-glycoprotein I-dependent aCL A positive lupus anticoagulant test, detected according to the guidelines of the ISTH (38)
Anti-b2GPI of IgG and/or IgM isotype in serum or plasma (in titre >99th percentile)
"Definite APS is considered to be present if at least one clinical and one laboratory criteria are met bPositivity should be present on two or more occasions at least 12 weeks apart for any of the tests
Miyakis S, Lockshin MD, Atsumi T, Branch DW, Brey RL, Cervera R et al (2006) International consensus statement on an update of the classification criteria for definite antiphospholipid syndrome (APS). J Thromb Haemost 4(2):295-306 Wilson WA, Gharavi AE, Koike T, Lockshin MD, Branch DW, Piette JC et al (1999) International consensus statement on preliminary classification criteria for definite antiphospholipid syndrome: report of an international workshop. Arthritis Rheum 42(7):1309-1311
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