Abstract
Antiphospholipid antibodies (aPL) are mandatory for the diagnosis but are also a risk factor for the antiphospholipid syndrome (APS) clinical manifestations. Lupus anticoagulant (LA), anticardiolipin (aCL), and anti-beta2 glycoprotein I (β2GPI) assays are the formal laboratory classification/diagnostic criteria. Additional nonclassification assays have been suggested; among them, antiphosphatidylserine-prothrombin (aPS/PT) and antidomain 1 β2GPI antibodies are the most promising ones although not yet formally accepted. aPL represent the example of a laboratory test that moved from dichotomous to quantitative results consistent with the idea that reporting quantitative data offers more diagnostic/prognostic information for both vascular and obstetric manifestations. Although the general rule is that the higher the aPL titer, the higher the test likelihood ratio, there is growing evidence that this is not the case for persistent low titers and obstetric events. LA displays the highest diagnostic/prognostic power, although some isolated LAs are apparently not associated with APS manifestations. Moreover, isotype characterization is also critical since IgG aPL are more diagnostic/prognostic than IgA or IgM. aPL are directed against two main autoantigens: β2GPI and PT. However, anti-β2GPI antibodies are more associated with the APS clinical spectrum. In addition, there is evidence that anti-β2GPI domain 1 antibodies display a stronger diagnostic/prognostic value. This finding supports the view that antigen and even epitope characterization represents a further step for improving the assay value. The strategy to improve aPL laboratory characterization is a lesson that can be translated to other autoantibody assays in order to improve our diagnostic and prognostic power.
Highlights
The antiphospholipid syndrome (APS) is formally defined as the association of arterial/venous thrombosis and/or recurrent miscarriages in the absence of any other known cause and the persistent presence of antiphospholipid antibodies detectable by solid-phase or functional coagulation assays (Table 1) [1]
The right choice and interpretation of the diagnostic aPL assays are pivotal to avoid the risk of an overdiagnosis, having in mind that both thrombosis and miscarriages are relatively frequent and due to several causes unrelated to aPL
These antibodies are not associated with APS manifestations and are not pathogenic in animal models; altogether this finding supports that they are not diagnostic aPL [35]
Summary
The antiphospholipid syndrome (APS) is formally defined as the association of arterial/venous thrombosis and/or recurrent miscarriages in the absence of any other known cause and the persistent presence of antiphospholipid antibodies (aPL) detectable by solid-phase (beta2 glycoprotein I [b2GPI]-dependent anticardiolipin [CL] and anti-b2GPI) or functional coagulation assays (lupus anticoagulant—LA) (Table 1) [1]. Medium/ high titers of aPL detectable by solid-phase assays (i.e., aCL and anti-b2GPI) or the positivity for two or three laboratory assays confer a higher risk for both vascular and obstetric events than low titer aPL or positivity in a single test only [5, 6].
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