Clinical characteristics of patients with systemic lupus erythematosus showing a false-positive result of syphilis screening

A false-positive result of syphilis screening test (FPST) is a characteristic finding in patients with systemic lupus erythematosus (SLE). We evaluated the clinical characteristics of SLE patients with FPST at SLE diagnosis. We reviewed the medical records of patients with SLE who underwent the Venereal Disease Research Laboratory or Rapid Plasma Reagin tests at SLE diagnosis at Severance Hospital between 2006 and 2016. The baseline characteristics and clinical outcomes were compared between patients with FPST and those with a negative result of syphilis screening test. Of 145 patients with SLE, 20 patients showed FPST and 125 patients showed a negative syphilis screening result. At SLE diagnosis, patients with a negative result had higher SLE disease activity index (5.0 vs. 8.0, P < 0.001) and were more commonly complicated with nephritis (15.0% vs. 41.6%, P = 0.026). High level of serum total protein (> 8 g/dL) and the presence of anti-cardiolipin antibodies were independently associated with FPST (P = 0.010 and 0.037, respectively). During the follow-up (median 61 months), 5 patients with FPST (20.0%) and 12 patients without FPST (9.6%) were finally diagnosed with APS. The long-term risk of de novo thrombosis was higher in the FPST group (n = 4/20, 20% vs n = 6/125, 4.8%, P = 0.041). However, all-cause mortality showed no difference between the FPST group and the negative group. Patients with SLE showing FPST showed lower disease activity at SLE diagnosis but higher thrombotic risk and similar overall survival compared to those without FPST.