[Nested-PCR for gene that encodes the antigen b applied to the diagnosis of pulmonary tuberculosis]

The polymerase chain reaction used for amplifying an internal sequence of a previously amplified fragment (nested-PCR) was investigated as a complementary alternative for searching for alcohol-acid resistant bacilli and Mycobacterium tuberculosis cultures in Lowenstein-Jensen medium. 144 sputum samples were investigated from patients with suspected tuberculosis that were sent to the Tuberculosis Laboratory of the Evandro Chagas Institute in Belém, between June 2002 and December 2003. From the 144 samples, 121 were characterized as tuberculosis: 119 were positive in cultures, 95 under bacilloscopy and 128 using nested-PCR. The sensibility of the nested-PCR was 96% (116/121), while the specificity was 48% (11/23). Nested-PCR may be a complementary tool for diagnosing tuberculosis, since it presents sensitivity equivalent to that of cultures. However, further evaluations are needed with the aim of minimizing the number of false-positive results.