Angiotensin-converting enzyme is increased in some cases of active sarcoidosis. Sensitivity about 75%, specificity about 95%. The sensitivity increases with the stage of the disease. Serial ACE determinations may be helpful in following the clinical course of sarcoidosis or to monitor the effectiveness of corticosteroid therapy. Elevated ACE levels will return to normal in sarcoidosis as a result of spontaneous or corticosteroid-induced remission. Decreased ACE activity is found in patients having chronic obstructive lung disease, lung cancer, emphysema, and cystic fibrosis. Patients with active tuberculosis generally have decreased activity though approximately 6% will show increases in ACE levels.