If pcr is positve and culture negative how do we go about it in tuberculosis?

On treatment or not?: Anti-tb therapy can do this and the pcr (done on respiratory secretions?) could be false positive. If one really though clinically that the person had tb, i'd likely believe the pcr.

Inadequate info: Has it been 6-8 weeks for the culture? What fluid was the testing done on? If sputum, was it processed appropriately? Was the pcr done in accredited lab? There is a possibility of sample contamination during the pcr test. Pcr positivity should be interpreted with caution in the presence of a negative culture. Talk to your doctor to address these questions.

PCR can be false pos: False positive. If the suspicion for TB is high then a positive pcr should probably be treated. But if the suspicion for TB is not high, then the pcr is more likely to be false positive in this situation. No test is perfect, and you have to weigh the risks and benefits of both courses of action.