Multi-center evaluation of the Abbott IMx SELECT(®) Chlamydia Blocking Reagent for verification of chlamydia trachomatis in female endocervical and male urethral swabs

The IMx Chlamydia Blocking Reagent (CBR) is used with the IMx SELECT Chlamydia assay to verify chlamydial antigen in reactive specimens. CBR performance was compared to resolved cell culture. Of 1,776 specimens tested with IMx, 230 reactive specimens were tested with CBR. Two hundred eight culture or direct fluorescent antibody (DFA) positive specimens were verified as positive with CBR. Seven culture/DFA negative specimens were reactive in IMx and verified as positive with CBR, Six of these specimens were available for polymerase chain reaction (PCR) testing and were PCR positive. Nine culture/DFA negative specimens were IMx reactive, but were verified as negative with CBR. Six culture or DFA positive specimens were verified as negative with CBR or were inconclusive. CBR improves the specificity of the IMx assay from 99.2% to 99.9% and increases the positive predictive value from 95.2% to 99.5%.