Abstract
Background Patients positive for all three types of antiphospholipid antibodies (aPLs; triple
positivity) have been identified for having a high risk for thrombotic events. However,
the clinical significance of isolated lupus anticoagulant (LAC) positivity is debated.
Objectives To investigate the clinical relevance of isolated LAC.
Methods A total of 456 patients were enrolled in this study; 66 antiphospholipid syndrome
patients and 390 control patients. The control group consisted of autoimmune patients
(n = 91), patients with thrombosis but without aPLs (n = 127), and normal controls (n = 172). LAC, anticardiolipin (anti-CL), and anti-β2 glycoprotein I (anti-β2GPI) immunoglobulin
G (IgG) and immunoglobulin M (IgM) were determined according to the International
Society on Thrombosis and Haemostasis (ISTH) guidelines. Anti-CL and anti-β2GPI were
measured by four different solid-phase platforms to overcome variability between test
systems. The noncriteria IgA anti-CL and anti-β2GPI, antidomain I of β2GPI IgG, and
antiphosphatidylserine/prothrombin antibodies (anti-PS/PT) IgG and IgM were detected
according to the ISTH guidelines for solid-phase assays.
Results In total, 70 patients were positive for LAC, of which 44 were negative for both anti-β2GPI
and anti-CL antibodies. We found that isolated LAC proved to be strongly associated
with vascular thrombosis (odds ratio [OR]: 7.3; 95% confidence interval [CI]: 3.3–16.1),
even better than triple-positive samples (OR: 4.3; 95% CI: 1.6–12.2). The titers of
the anti-PS/PT IgG and IgM were significantly higher in triple-positivity samples
compared with samples with isolated LAC positivity. The majority of single LAC positives
were anti-PS/PT-negative. We observed that LAC positivity was weaker in isolated LAC-positive
patients compared with LAC activity in triple-positive patients.
Conclusion Isolated LAC was highly associated with thrombosis. The presence of anti-PS/PT antibodies
could not explain LAC positivity in isolated LAC. Isolated LAC showed a weaker LAC
activity compared with triple-positive patients.
Keywords
antiphospholipid antibodies - β2 glycoprotein I - lupus anticoagulant - prothrombin
- thrombosis