Fecal polymerase chain reaction for Mycobacterium tuberculosis IS6110 to distinguish Crohn's disease from intestinal tuberculosis

Background: We have previously shown that amplification of Mycobacterium tuberculosis specific DNA (TB PCR) from feces reliably diagnosed intestinal tuberculosis. This study was undertaken to determine how well this test would distinguish intestinal tuberculosis from Crohn's disease in a country endemic for tuberculosis. Methods: Consecutive patients with diagnoses of Crohn's disease and intestinal tuberculosis were enrolled, and the diagnoses confirmed by follow up. DNA was extracted from fecal samples and subjected to polymerase chain reaction TB PCR for IS6110 sequence which is specific for M. tuberculosis. Results: Twenty one of 24 patients with intestinal tuberculosis and 5 of 44 patients with Crohn's disease tested positive by TB PCR. The sensitivity, specificity, positive predictive and negative predictive values for TB PCR in distinguishing tuberculosis from Crohn's disease were 0.79 (95% confidence interval 0.57-0.92), 0.88 (0.75-0.96), 0.79 (0.57-0.92) and 0.88 (0.75-0.96), respectively. A combination of fecal TB PCR with mycobacterial culture of mucosal biopsy specimens identified 23 of 24 (96.2%) of patients with intestinal TB, with sensitivity, specificity, positive predictive and negative predictive values (95% CI) of 0.95 (0.78-0.99), 0.88 (0.75-0.96), 0.82 (0.63-0.93) and 0.97 (0.86-0.99), respectively. Conclusion Fecal TB PCR is a good screening test to distinguish intestinal tuberculosis from Crohn's disease