Background: Tuberculosis is still one of the most important causes of mortality and morbidity in many countries and is the second only to human immunodeficiency virus as a cause of death worldwide resulting from a single infectious agent. In 1993, the World Health Organization declared tuberculosis a global public health emergency. Conven-tional methods for the diagnosis of Mycobacterium tuberculosis (MTB) infections are time consuming, as MTB culture requires 3-8 weeks for growth. To determine the sensitivity of polymerase chain reaction (PCR) in peripheral blood mononuclear cells (PBMC), we have evaluated Mycobacterium tuberculosis DNA in peripheral blood samples with PCR technique in adults with new cases of pulmonary and extra-pulmonary tuberculosis. Setting: Department of Infectious disease of Imam Khomeini Hospital, 2004- 2005, Tehran, Iran.

Methods: In this cross-sectional study, we evaluated MTB DNA extracted from 3ml citrated peripheral blood samples from 95 adults with new cases of pulmonary and extra-pulmonary tuberculosis. DNA extraction was performed using a commercial PCR kit with IS1081 primers. For prevention of cross contamination and reduction of false positives, all steps were performed under laminar hood.

Results: The 95 patients, 59 of whom were male, had a mean age 44.44 years (SD±20.26); 69 cases had pulmonary and 26 had extra-pulmonary tuberculosis. PCR was positive in 32 (33.7%) patients and negative in 63 (66.3%) cases. The overall sensitivity and accuracy of the PCR assay was 44.1% for pulmonary, 19.2% for extra-pulmonary and 10% for disseminated tuberculosis, respectively.

Conclusion: The low sensitivity of the IS1081 primer MTB-PCR assay on PBMC may pose problems for the rapid diagnosis of tuberculosis. However, further studies are needed to confirm this technique as an alternative test for the diagnosis of tuberculosis.