PCR colorimetric dot-blot assay and clinical pretest probability for diagnosis of Pulmonary Tuberculosis in smear-negative patients.
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 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.


CONCLUSIONS
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.
Scherer
Luciene Cardoso
LC
Programa de pós Graduação em Ciências Biológicas- Bioquímica, Universidade Federal do Rio Grande do Sul-UFRGS, Porto Alegre, RS, Brazil. luciene.scherer@hotmail.com
Sperhacke
Rosa Dea
RD
Jarczewski
Carla
C
Cafrune
Patrícia I
PI
Minghelli
Simone
S
Ribeiro
Marta Osório
MO
Mello
Fernanda Cq
FC
Ruffino-Netto
Antonio
A
Rossetti
Maria Lr
ML
Kritski
Afrânio L
AL
D000328:Adult; D001938:Brazil; D003124:Colorimetry; D003371:Cough; D004269:DNA, Bacterial / Q000032:analysis*; D003906:Developing Countries; D006801:Humans; D015336:Molecular Probe Techniques; D009169:Mycobacterium tuberculosis / Q000235:genetics* / Q000302:isolation & purification; D009710:Nucleotide Mapping; D016133:Polymerase Chain Reaction / Q000379:methods*; D011336:Probability; D012680:Sensitivity and Specificity; D013183:Sputum / Q000382:microbiology; D014397:Tuberculosis, Pulmonary / Q000175:diagnosis* / Q000453:epidemiology / Q000382:microbiology
D004269:DNA, Bacterial