Chest radiographs during isoniazid therapy.

For most tuberculin reactors, chest radiographs are obtained at the beginning of, at various intervals through the course of, and at the end of the year of isoniazid preventive therapy. A study of 1,524 tuberculin reactors was performed to determine the value of chest radiographs obtained after therapy was begun; 1,315 had normal radiographs at the beginning and end of therapy, and 209 had radiographic abnormalities at both times. No significant changes were noted in any of the 1,524 patients' radiographs. Similar results had been reported for 551 tuberculin reactors in an earlier study. This provides a total of 2,075 patients for whom no value could be found in the subsequent radiographs. We found no value in repeating normal chest radiographs of positive reactors if they had completed at least 9 months of the properly recommended 12 months of isoniazid preventive therapy. The lack of value of repeat radiographs, coupled with their fixed cost and the potential risk of unnecessary radiation, dictated our change in policy--we no longer repeat normal chest radiographs in such persons.