In a Prospective Inceptional Cohort Study of Children with Thrombosis, a Persistently Positive Dilute Russell Viper Venom Time Is Associated with Thrombus Progression or Recurrence and Multiple Antiphospholipid Antibodies

BACKGROUND: Antiphospholipid antibodies (APA) that persist ≥12 weeks in adults with acute thrombosis are predictive of thrombus recurrence. The significance of APA in children with thrombosis is unclear. This study was developed to examine the relationship of a persistently positive lupus anticoagulant (≥ 12 weeks), assessed by the dilute Russell Viper Venom Time (dRVVT), to adverse thrombus outcomes including progression or recurrence. In addition, the relationship of a persistently positive dRVVT to the prevalence and titer of several other APA in children with thrombosis were examined.

METHODS: Data from a consented prospective inceptional cohort study of pediatric thrombosis and thrombophilia (COMIRB 05–0339) were extracted for this analytic project. Eligibility included age ≤ 21 years at presentation, objectively confirmed thrombus, dRVVT within 4 weeks of presentation and repeated ≥ 12 weeks later. Patients with a persistently positive dRVVT (ratio of Screen/Confirm ≥1.2) were classified as having antiphospholipid syndrome (APS positive), and those with a negative dRVVT were classified as APS negative. Twelve or more weeks from presentation, patient plasmas were tested in ELISA assays for the presence and titer of IgM and IgG antibodies directed against protein C (PC), protein S (PS), prothrombin (II), β-2-Glycoprotein I (B2GPI), and cardiolipin (ACA). A euglobulin clot lysis assay (ELT) and hexagonal (II) phase phospholipid assay (STACLOT LA, Diagnostica Stago, Inc.) were also performed.

RESULTS: The cohort included 122 cases with thrombosis. Of these, 35 failed eligibility due to transient dRVVT positivity or lack of blood sampling within the specified time period. Of the remaining 87 patients, 43 were APS positive and 44 were APS negative. APS positivity was associated with longer duration of therapy (p<0.001) and multiple autoantibodies at ≥ 12 weeks from presentation (p=0.04). APS was associated with higher titers of several antibodies, including those directed against: B2GPI (IgG, p=0.01), II (IgG, p=0.02), PC (IgG, p=0.03; IgM, p<0.001). Despite the longer duration of therapy for these patients, APS was highly associated with thrombus progression or recurrence (47% in APS positive versus 8% in APS negative, p=0.001). Thrombus progression or recurrence was further associated with positivity for ACA IgM, Anti-II IgM and the STACLOT LA (p=0.02 for each), and additionally with higher titers of antibodies against B2GPI (IgG, p=0.03), II (IgM, p=0.05), PC (IgM, p=0.04), and PS (IgM, p=0.03).

CONCLUSION: In this pediatric prospective inceptional cohort study, APS (defined as a persistence of positive dRVVT 12 weeks or greater in children affected with thrombosis), was found in more than one third of children and was associated with higher prevalence and titers of several APA. In spite of longer duration of therapy, children with APS had a significantly higher rate of thrombus progression or recurrence. APA testing in children with thrombosis is important to predict outcomes. Future clinical trials must consider APS status in evaluating risk-stratified therapy for thrombotic diseases in children.