Obstetric antiphospholipid syndrome: a recent classification for an old defined disorder

Obstetric antiphospholipid syndrome (APS) is now being recognized as a distinct entity from vascular APS. Pregnancy morbidity includes >3 consecutive and spontaneous early miscarriages before 10weeks of gestation; at least one unexplained fetal death after the 10th week of gestation of a morphologically normal fetus; a premature birth before the 34th week of gestation of a normal neonate due to eclampsia or severe pre-eclampsia or placental insufficiency. It is not well understood how antiphospholipid antibodies (aPLs), beyond their diagnostic and prognostic role, contribute to pregnancy manifestations. Indeed aPL-mediated thrombotic events cannot explain the obstetric manifestations and additional pathogenic mechanisms, such as a placental aPL mediated complement activation and a direct effect of aPLs on placental development, have been reported. Still debated is the possible association between aPLs and infertility and the effect of maternal autoantibodies on non-vascular manifestations in the babies. Combination of low dose aspirin and unfractionated or low molecular weight heparin is the effective treatment in most of the cases. However, pregnancy complications, in spite of this therapy, can occur in up to 20% of the patients. Novel alternative therapies able to abrogate the aPL pathogenic action either by interfering with aPL binding at the placental level or by inhibiting the aPL-mediated detrimental effect are under active investigation.

Confirmation of initial antiphospholipid antibody positivity depends on the antiphospholipid antibody profile

BACKGROUND

The revised classification criteria for the antiphospholipid syndrome state that antiphospholipid (aPL) antibodies (lupus anticoagulant [LAC] and/or anticardiolipin [aCL] and/or anti-β2 -glycoprotein I [aβ2 GPI] antibodies) should be detected on two or more occasions at least 12 weeks apart. Consequently, classification of patient risk and adequacy of treatment may be deferred by 3 months.

OBJECTIVES

In order to early classify patient risk, we evaluated whether aPL positivity confirmation is related to aPL antibody profiles.

PATIENTS AND METHODS

Consecutive patients referred to our center who were initially positive in one or more tests exploring the presence of aPL were tested after 3 months. During a 4-year period, 225 patients were initially positive in one or more tests, and 161 were available for confirmation after 3 months. Patients were classified as triple-positive (n = 54: LAC(+) , aCL(+) , aβ2 GPI(+) , same isotype), double-positive (n = 50: LAC(-) , aCL(+) , aβ2 GPI(+) , same isotype) and single-positive (n = 53: LAC or aCL or aβ2 GPI antibodies as the sole positive test).

RESULTS

Among subjects with triple positivity at initial testing, 98% (53 of 54) had their aPL profile confirmed after 12 weeks. The double-positive and single-positive groups had data confirmed in 42 of 50 (84%) and 23 of 57 (40%) subjects, respectively.

CONCLUSIONS

Our results show that high-risk subjects with triple-positive aPL profiles are identified early, at the time of the initial screening tests.

Antiphospholipid antibodies: evaluation of the thrombotic risk

The laboratory diagnosis of the antiphospholipid syndrome (APS) via antiphospholipid antibody (aPL) tests, including lupus anticoagulant (LAC), anti-cardiolipin (aCL), or anti-beta2 glycoprotein I (aβ2GPI) antibodies remains a challenge. Coagulation tests for LAC as well as solid phase assays for aCL and aβ2GPI have methodological shortcomings, although for LAC large progress have been made in standardization. All assays are associated with clinical APS-criteria (thrombotic and/or pregnancy complications) but with limited specificity. Besides, clinical studies demonstrating the association between the presence of aPL and thrombosis are not always well designed and result in wide ranges of odds ratio with large variation between studies. The best association between thrombotic complications and aPL is found for LAC. The association between thrombosis and aCL or aβ2GPI is at least inconsistent. The inclusion of more specific assays, such as the domain-I-β2GPI.antibodies is too premature and depends on further investigation in large clinical studies and the commercial availability. The search for new assays should proceed to identify patients with aPL with increased risk for thrombosis, preferable in large prospective studies. Meanwhile, with the current available LAC, aCL and aβ2GPI assays it is strongly recommended to make antibody profiles. Multiple positivity of tests seems clinically more relevant. The strengths and weaknesses of the current laboratory criteria for APS are discussed in view of their role in risk stratification of patients with thrombotic events.