CD7 and syphilis: Using the widely accepted TPPA as the gold standard for sensitivity and specificity, Tp40-ELISA showed a sensitivity of 97.20%, specificity of 96.85%, positive predictive value of 96.30%, negative predictive value of 97.20%, and an overall agreement rate of 97.01% (Table 3), which indicates a good clinical diagnostic value for Tp40-ELISA in syphilis.