Dynamics of the laboratory results in patients with pulmonary tuberculosis

The process of infection and disease development is difficult to follow-up before tuberculosis (TB) confirmation. The laboratory analysis mirrors the infection with the possible subsequent breakdown to clinical TB. To better define the dynamics of the laboratory results in suspected and already confirmed patients with pulmonary TB, we studied the analysis of 1467 pathologic samples collected during the hospitalization of 841 patients. The samples were analyzed by 3 laboratory methods--direct microscopy, culture, and polymerase chain reaction (PCR). It was found that compared to cultures, the PCR method is more sensitive. For few cases, we demonstrate that the PCR result is positive about 2 weeks before the first positive culture. During the treatment follow-up, the PCR result remains positive for a long time, up to 4 to 5 months after the last positive culture. For better definition of the period during which microscopy and culture results remain positive, we studied the laboratory results of 100 casually selected patients with pulmonary TB positive on culture. The median periods during which these patients were found to be microscopy and culture positive were 10 and 25 days, respectively. Second to the dynamics of the laboratory results, we demonstrate that TB development is very rapid, whereas the period of recovery is long. The PCR results have to be reproducibly negative to accept that the process of active therapy is completed and the patient can remain under surveillance. On the basis of the laboratory data obtained, we propose empiric models for the dynamics of the laboratory results for patients with pulmonary tuberculosis.