CD40LG and syphilis: In these studies, PCR was less sensitive because it detected fewer cases than serologic tests.18,19,21 In another study, only 35% of these children had positive CSF syphilis identified by PCR.21 On the other hand, 13 of 14 children with positive PCR for syphilis in CSF (93%) had positive serum IgM immunoblotting results.