SERUM ANGIOTENSIN-CONVERTING ENZYME-ACTIVITY, CONCENTRATION, AND SPECIFIC ACTIVITY IN GRANULOMATOUS INTERSTITIAL LUNG-DISEASE, TUBERCULOSIS, AND COPD

Angiotensin-converting enzyme (ACE) activity in serum is used as an ai d to the diagnosis and follow-up of patients with sarcoidosis. A theor etical limitation of measurements of activity is that these may be aff ected by the presence of pharmacologic or endogenous inhibitors of ACE , Immunoassays of ACE concentration avoid this problem and, when combi ned with tests of ACE activity, permit calculation of specific activit y of ACE. In this study, we set out to develop a sensitive radioimmuno assay for ACE to compare results obtained with this method with result s of ACE activity and calculated ACE specific activity in patients suf fering from a variety of lung diseases. In a group of control subjects (n=32), the ACE concentration was 453.7 +/- 159.8 (SD) ng/mL; 95% con fidence interval (CI), 398.34 to 509.06, but levels were significantly elevated in sarcoidosis (979.3 +/- 558.6 ng/mL; 95% CI, 827.5 to 1,13 1.1; n=51; p<0.001 vs control subjects), silicosis (646.5 +/- 239.1 ng /mL; 95% CI, 544.2 to 748.8; n=21; p<0.01), and miliary tuberculosis ( 647.0 +/- 217.1 ng/mL; 95% CI, 551.9 to 742.1; n=29; p<0.01). The leve ls were normal in COPD, interstitial pulmonary fibrosis, and active ca vitary pulmonary tuberculosis. The overall correlation between ACE act ivity and concentration measurements was strong (r=0.93), No evidence of endogenous ACE inhibition was observed in any of the disease catego ries studied except in COPD where an elevation of ACE specific activit y was observed, raising the possibility that in this condition differe nt isozymes of ACE with higher specific activity might be released.