Influence of different IgG anticardiolipin antibody cut‐off values on antiphospholipid syndrome classification

Abstract

Summary. Background: While medium to high titers of anticardiolipin (aCL) antibodies, defined as >40 GPL units or >99th percentile, is a laboratory criteria for the ÔdefiniteÕ diagnosis of antiphospholipid syndrome (APS), agreement between the two cut-offs has not been validated. Objective: To validate the current aCL laboratory criterion by verifying the effect of the two cut-offs on APS classification. Patients/ methods: Ninety aCL positive APS patients were selected on the basis of their GPL values above the 99th percentile (17.4 GPL), which was calculated by testing 100 age-and sex-matched healthy subjects. Results: A significant difference in the IgG positivity (P < 0.0001) was found between the APS laboratory profiles as 20 out of the 24 (83.3%) patients with single positivity (aCL alone), six out of the 23 (26.1%) with double positivity (aCL plus lupus anticoagulant or anti-b 2 glycoprotein I), and none out of the 43 with triple positivity (aCL plus lupus anticoagulant and anti-b 2 glycoprotein I) had titers between the 99th percentile and 40 GPL units. Moreover, the rate of aCL values between the 99th percentile and 40 GPL units was significantly higher (P < 0.0001) in patients with pregnancy morbidity (73.7%) as compared to those with vascular thrombosis (16.9%) and those with both conditions (16.7%). Conclusion: The 99th percentile cut-off level seems more sensitive than the >40 GPL value for APS classification, as it includes subjects with aCL positivity alone as well as patients with pregnancy morbidity.

Definition and significance of high positivity aCL ELISA

“…In two recent studies Ruffatti et al and Devreese et al show that the 99th percentile of controls is not sufficient to define an optimal cut-off. 8,9 Most patients with clinical manifestations of APS have higher aCL values. 8,9 Moreover the 99th percentile of normal controls and 40 GPL units are not equivalent.…”

“…8,9 Most patients with clinical manifestations of APS have higher aCL values. 8,9 Moreover the 99th percentile of normal controls and 40 GPL units are not equivalent. 8,9 To identify high positivity it is possible to use a threshold defined by the 99th percentile of disease controls.…”

Antiphospholipid syndrome: laboratory detection, mechanisms of action and treatment

“…The difference in the results may depend on the differences in the selected cohorts as the risk of pregnancy loss is low in LA-negative patients [89]. In addition, most patients diagnosed with primary obstetric APS are only aCL positive [90]. Until evidence from clinical trials enroling patients with a uniform aPL profile (confirmed in a reference laboratory) becomes available, obstetric (alone) complications in LA-negative patients should be treated with a prophylactic dose of LMWH and lowdose aspirin.…”

Obstetric Antiphospholipid Syndrome: Lobsters Only? Or Should We Also Look for Selected Red Herrings?

“…The Journal of on May 11, 2018 -Published by www.jrheum.org Downloaded from patients with thrombotic APS (16.9%) and those with both conditions (16.7%) 13 . Consistently, pregnancy outcomes in untreated patients with low aPL levels and APS-like obstetrical events are similar to women with classical APS; moreover, conventional treatment with LDASA with or without LMWH improved pregnancy outcomes to an extent comparable to otherwise healthy women with REM 14 .…”