Is an FEV 1 of 80% predicted a normal spirometry in cystic fibrosis children and adults?

FEV 1 is considered the gold standard spirometric measure for the assessment and management of cystic fibrosis lung disease. Recent evidence suggests that tests at lower lung volumes may be more sensitive. Objectives To assess how many other spirometric tests are abnormal in the presence of a normal FEV 1 (≥80%) and which spirometric tests are most sensitive in detecting airway obstruction. Methods This was a retrospective analysis of 3169 spirometry tests on 184 patients with cystic fibrosis aged 6‐57 years. Tests were acceptable if they met ATS criteria. Results Tests with normal FEV 1 , FEF 75 showed obstruction in 58% of tests, FEF 25‐75 in 31% and FEV 1 /FVC ratio in 72%. Overall 75% of tests had an abnormality. FEF 75 , FEF 25‐75 , FEF 50 and FEV 1 /FVC ratio were all significantly more sensitive in identifying obstruction than FEV 1 . The FEV 1 /FVC ratio was the most sensitive of all tests in identifying obstruction except in adults (> 20 years), in whom FEF 75 at 90%, was more sensitive than the ratio at 85%. FEF 25‐75 was also at 85% sensitive. Even though the FEV 1 /FVC ratio was the most sensitive of all tests, in the presence of a normal ratio, 35% other tests were abnormal. Conclusions Normal FEV 1 , is not indicative of normal spirometry. FEV 1 /FVC is the most sensitive measure of early or mild airway obstruction in children with cystic fibrosis. If only the FEV 1 /FVC ratio was considered, many cases of obstruction would be missed, therefore all spirometric measures should be considered in the clinical evaluation of airway obstruction.