BMC Public Health 2007, 7:356 http://www.biomedcentral.com/1471-2458/7/356 An increased sensitivity of PCR, when used in parallel with the high pretest probability, was observed in non- previously treated patients, compared to those who had had previous anti-TB treatment (sensitivity: 91% vs 83%). Similar results were found in HIV seropositive study sub- jects, in which the sensitivity was 91% among non-previ- ously treated cases and 89% among those treated in the past. In HIV seronegative suspects, similar results were observed, in which sensitivity was 93% among non-previ- ously treated cases and 83% among those treated in the past. An increased specificity of PCR associated with a high pre- test probability was observed in non-previously treated patients, compared to those who had previous anti-TB treatment (specificity: 79% vs 61%). Similar results were found in HIV seropositive study subjects: specificity was 79% among non-previously treated cases and 75% among those treated in the past. In HIV seronegative subjects, using the same diagnostic test, the specificity was 80% among non-previously treated cases and 62% among those treated in the past. Assuming different TB prevalence scenarios, the use of the PCR colorimetric dot-blot in parallel with a high clinical suspicion of SNPTB showed similar positive and negative PVs, among HIV seropositive and HIV seronegative patients (Figure 1). In regions from developing nations with a estimated TB prevalence of 5%–10%, described in out-patient units attending persons with coughs for more than three weeks (respiratory symptomatic, according to WHO), NPV for the PCR colorimetric dot-blot technique lSFeiimngcuelraretaiot1ensof positive and negative predictive values of ZN and Culture/PCR dot-blot tests, according to different TB preva- Simulation of positive and negative predictive values of ZN and Culture/PCR dot-blot tests, according to dif- ferent TB prevalence rates. PPV: Positive Predictive Value, NPV: Negative Predictive Value, PP: pretest probability (clinical suspicion); TB prevalence rates: from 5% to 48.8% Page 6 of 10 (page number not for citation purposes)