Exhaled carbon monoxide in sarcoidosis.

BACKGROUND Exhaled Carbon monoxide has been proposed as a non-invasive marker in several inflammatory diseases of the lung, but no data are available in patients with sarcoidosis. METHODS We evaluated the levels of exhaled CO in 78 nonsmoker patients with sarcoidosis and we compared the results with 25 healthy non smoker controls, of 25 patients with a variety of interstitial lung diseases, and 77 smokers. RESULTS Mean value of exhaled CO in sarcoidosis was 3.3 (2.9-3.8) ppm (GM with 95% CI in parenthesis), resulting significantly higher than both normal controls, 1.4 (1.2-1.7) ppm (p<0.001), and clinical controls, 2.1 (1.7-2.7) ppm (p<0.02). All these levels, however, were markedly lower than those observed in smokers, 14.6 (12.7-16.9) ppm. No correlation was found with radiological stage, steroid therapy, respiratory function, or serum ACE activity. Using an upper normal value of 4 ppm, an increased level of exhaled CO was found in 50% of patients with sarcoidosis, in 24% of clinical controls, and in 97% of smokers. CONCLUSIONS Our data indicate that significant release of endogenous CO occurs in sarcoidosis. It is unlikely that the measurement of exhaled CO could be of diagnostic usefulness, due to its low specificity and to the possible influence by occasional or passive smoke.