BMC Public Health Research article PCR colorimetric dot-blot assay and clinical pretest probability for diagnosis of Pulmonary Tuberculosis in Smear-Negative patients Luciene Cardoso Scherer*†1,3, Rosa Dea Sperhacke2, Carla Jarczewski5, Patrícia I Cafrune2, Simone Minghelli6, Marta Osório Ribeiro6, Fernanda CQ Mello4, Antonio Ruffino-Netto7, Maria LR Rossetti2,3 and Afrânio L Kritski†4 BioMed Central Open Access Address: 1Programa de pós Graduação em Ciências Biológicas- Bioquímica, Universidade Federal do Rio Grande do Sul-UFRGS, Porto Alegre, RS, Brazil, 2Centro de Desenvolvimento de Ciência e Tecnologia- CDCT, Fundação Estadual de Produção e Pesquisa em Saúde-FEPPS/RS, Porto Alegre, RS, Brazil, 3Universidade Luterana do Brasil-ULBRA, Canoas, RS, Brazil, 4Unidade de Pesquisa em Tuberculose, Hospital Universitário Clementino Fraga Filho, UPT/HUCFF, Universidade Federal do Rio de Janeiro-UFRJ, Rio de Janeiro, RJ, Brazil, 5Hospital Sanatório Partenon/Secretaria da Saúde do Rio Grande do Sul, Porto Alegre, RS, Brazil, 6State 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 and 7Faculdade de Medicina de Ribeirão Preto, Universidade de São Paulo, SP, Brazil Email: Luciene Cardoso Scherer* - luciene.scherer@hotmail.com; Rosa Dea Sperhacke - deasperhacke@hotmail.com; Carla Jarczewski - jarczews@terra.com.br; Patrícia I Cafrune - patricia_cafrune@hotmail.com; Simone Minghelli - sminghelli@terra.com.br; Marta Osório Ribeiro - martaoso@terra.com.br; Fernanda CQ Mello - fcqmello@hucff.ufrj.br; Antonio Ruffino-Netto - aruffino@fmrp.usp.br; Maria LR Rossetti - mrossett@terra.com.br; Afrânio L Kritski - kritskia@gmail.com * Corresponding author †Equal contributors Published: 20 December 2007 BMC Public Health 2007, 7:356 doi:10.1186/1471-2458-7-356 This article is available from: http://www.biomedcentral.com/1471-2458/7/356 Received: 14 November 2006 Accepted: 20 December 2007 © 2007 Scherer et al; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Abstract Background: 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. Methods: 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. Results: 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 Page 1 of 10 (page number not for citation purposes)