Investigating Two-stage Tuberculin Skin Test for Screening Latent Tuberculosis Infections in Diabetic Patients: A Regional Study in Khorramabad, Iran

Introduction: latent tuberculosis infections (LTBI) are not detectable by a single-stage tuberculin test and maybe detected after repeating tests 7-21 days later. This phenomenon, called the boosting phenomenon, supports a two-stage test to identify false negatives in a single-stage test. The present study investigates the value of a two-stage tuberculin test in diabetic patients. Methods: We performed a tuberculin test for 195 diabetic patients. The patients with induration > 10 mm were subjected to a second tuberculin test 7-21 days later. Results: Of 195 patients, 115 came for measuring the tuberculin test induration, which was positive in 3 out of 115 patients (2.61%). Of the remaining 112 patients, 53 patients were subjected to the second test, and 38 patients came back for measuring the induration, which became positive in 4 (10.52%) patients. Conclusion: The increased LTBI rate from 2.61% to 10.52% following the second tuberculin test indicates a boosting phenomenon due to a delayed hypersensitivity reaction. Hence, patients with latent tuberculosis who had a false negative test in the first stage were identified.