Open Access Research article

PCR colorimetric dot-blot assay and clinical pretest probability for diagnosis of Pulmonary Tuberculosis in Smear-Negative patients

Luciene Cardoso Scherer13*, Rosa Dea Sperhacke2, Carla Jarczewski5, Patrícia I Cafrune2, Simone Minghelli6, Marta Osório Ribeiro6, Fernanda CQ Mello4, Antonio Ruffino-Netto7, Maria LR Rossetti23 and Afrânio L Kritski4

Author Affiliations

1 Programa de pós Graduação em Ciências Biológicas- Bioquímica, Universidade Federal do Rio Grande do Sul-UFRGS, Porto Alegre, RS, Brazil

2 Centro de Desenvolvimento de Ciência e Tecnologia- CDCT, Fundação Estadual de Produção e Pesquisa em Saúde-FEPPS/RS, Porto Alegre, RS, Brazil

3 Universidade Luterana do Brasil-ULBRA, Canoas, RS, Brazil

4 Unidade de Pesquisa em Tuberculose, Hospital Universitário Clementino Fraga Filho, UPT/HUCFF, Universidade Federal do Rio de Janeiro-UFRJ, Rio de Janeiro, RJ, Brazil

5 Hospital Sanatório Partenon/Secretaria da Saúde do Rio Grande do Sul, Porto Alegre, RS, Brazil

6 State Reference Laboratory (Laboratório Central do Rio Grande do Sul- Lacen, RS), Fundação Estadual de Produção e Pesquisa em Saúde-FEPPS/RS) Porto Alegre, RS, Brazil

7 Faculdade de Medicina de Ribeirão Preto, Universidade de São Paulo, SP, Brazil

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BMC Public Health 2007, 7:356  doi:10.1186/1471-2458-7-356

Published: 20 December 2007



Smear-negative pulmonary tuberculosis (SNPTB) accounts for 30% of Pulmonary Tuberculosis (PTB) cases reported annually in developing nations. Polymerase chain reaction (PCR) may provide an alternative for the rapid detection of Mycobacterium tuberculosis (MTB); however little data are available regarding the clinical utility of PCR in SNPTB, in a setting with a high burden of TB/HIV co-infection.


To evaluate the performance of the PCR dot-blot in parallel with pretest probability (Clinical Suspicion) in patients suspected of having SNPTB, a prospective study of 213 individuals with clinical and radiological suspicion of SNPTB was carried out from May 2003 to May 2004, in a TB/HIV reference hospital. Respiratory specialists estimated the pretest probability of active disease into high, intermediate, low categories. Expectorated sputum was examined by direct microscopy (Ziehl-Neelsen staining), culture (Lowenstein Jensen) and PCR dot-blot. Gold standard was based on culture positivity combined with the clinical definition of PTB.


In smear-negative and HIV subjects, active PTB was diagnosed in 28.4% (43/151) and 42.2% (19/45), respectively. In the high, intermediate and low pretest probability categories active PTB was diagnosed in 67.4% (31/46), 24% (6/25), 7.5% (6/80), respectively. PCR had sensitivity of 65% (CI 95%: 50%–78%) and specificity of 83% (CI 95%: 75%–89%). There was no difference in the sensitivity of PCR in relation to HIV status. PCR sensitivity and specificity among non-previously TB treated and those treated in the past were, respectively: 69%, 43%, 85% and 80%. The high pretest probability, when used as a diagnostic test, had sensitivity of 72% (CI 95%:57%–84%) and specificity of 86% (CI 95%:78%–92%). Using the PCR dot-blot in parallel with high pretest probability as a diagnostic test, sensitivity, specificity, positive and negative predictive values were: 90%, 71%, 75%, and 88%, respectively. Among non-previously TB treated and HIV subjects, this approach had sensitivity, specificity, positive and negative predictive values of 91%, 79%, 81%, 90%, and 90%, 65%, 72%, 88%, respectively.


PCR dot-blot associated with a high clinical suspicion may provide an important contribution to the diagnosis of SNPTB mainly in patients that have not been previously treated attended at a TB/HIV reference hospital.