Circulating anticoagulant and serological tests for syphilis.

Circulating anticoagulant (CA) and particularly lupus anticoagulant are commonly associated with biological false-positive tests for syphilis (BFP-STS) in patients with collagen diseases. CA was presently found in the sera of 8 out of 30 subjects with chronic BFP-STS without collagen or autoimmune diseases. It was not found in any of the 21 patients with various stages of syphilis. In 5 out of 21 elderly subjects (age greater than 70 years) in whom a positive BFP-STS was detected, there was no CA. It is concluded that the association between CA and BFP-STS is found only in patients with collagen and autoimmune diseases and in some of the younger chronic BFP-STS reactors. It is not detected in syphilitic patients or elderly subjects in whom a high incidence of BFP-STS can be found. The difference in the incidence of this association is probably due to the differing biologic behaviour of these autoantibodies.