Rheumatoid factor in congenital syphilis.

The rheumatoid factor (RF) latex test was evaluated as a test for congenital syphilis. High risk newborns of mothers with untreated or inadequately treated syphilis were studied. The asymptomatic infants were followed up for between 3 and 4 months (or longer if the VDRL test was positive). The overall performance of the RF latex test was better than that of the other tests studied, even though the sensitivity was 46.7%. The specificity and positive predictive value of the test were 100% whilst the negative predictive value was 86.4%. The test was negative in all 84 controls studied. Although a negative RF latex test cannot be used to exclude congenital syphilis in an asymptomatic infant, a positive test in the presence of maternal syphilis should lead one to strongly suspect congenital syphilis.