In the majority of women, Chlamydia trachomatis infections remain asymptomatic. These unrecognized and untreated infections may increase the risk for tubal factor subfertility at a later age. Since the association between C. trachomatis IgG antibodies in serum and tubal pathology was noticed, C. trachomatis IgG antibody testing has been used as a screening test for tubal factor subfertility. The diagnostic accuracy of C. trachomatis IgG antibody testing is limited, however. Since women who have persistent chlamydia infections are considered to be at the highest risk for developing late sequelae, the predictive value of markers of persistent infections have been studied in subfertile women. Patients who had C. trachomatis IgG antibodies (as markers of a previous infection), and an elevated C-reactive protein within the normal range (as a marker of a persisting infection) had the highest risk for having tubal pathology.