Background: The present study evaluated purified protein derivative (PPD) changes based on mediastinal lymph node density. Methods: This cross-sectional observational study was performed on 130 patients who were referred to Valiasr and Amir Al-Momenin Hospitals in Arak, Iran for a CT scan for non-infectious and non-tumor reasons. The gender of the patients was recorded, and they then underwent non-contrast CT, and their mediastinal lymph node density was measured and recorded based on the Hounsfield units. Patients were evaluated for changes in the tuberculin test. The induration diameter obtained from the tuberculin test was recorded for each individual. Data analysis was then carried out using SPSS software ver. 20. Results: There was a positive correlation between mediastinal lymph node density and tuberculin test induration diameter, so larger induration diameter in the tuberculin test results in increasing lymph node density result (r = 0.429, P < 0.001). There was a negative correlation between mediastinal lymph node density and age, i.e., mediastinal lymph node density decreased with increasing age (P < 0.001, r = -0.616). Lymph node density was higher in men than in women (P = 0.022). Conclusions: There is a positive correlation between the mediastinal lymph node density and the tuberculin test induration diameter, and the tuberculin test induration diameter increases with increasing lymph node density. There is a negative correlation between the mediastinal lymph node density and age, i.e., the mediastinal lymph node density decreases with increasing age. Lymph node density was also higher in men than in women. Therefore, the results can help ensure an earlier diagnosis of pulmonary tuberculosis, and measuring the mediastinal lymph node density is recommended.