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

INTRODUCTION: FEV1 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 FEV1 (≥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 FEV1 , FEF75 showed obstruction in 58% of tests, FEF25-75 in 31% and FEV1 /FVC ratio in 72%. Overall 75% of tests had an abnormality. FEF75 , FEF25-75 , FEF50 and FEV1 /FVC ratio were all significantly more sensitive in identifying obstruction than FEV1 . The FEV1 /FVC ratio was the most sensitive of all tests in identifying obstruction except in adults (> 20 years), in whom FEF75 at 90%, was more sensitive than the ratio at 85%. FEF25-75 was also at 85% sensitive. Even though the FEV1 /FVC ratio was the most sensitive of all tests, in the presence of a normal ratio, 35% other tests were abnormal.

CONCLUSIONS: Normal FEV1 , is not indicative of normal spirometry. FEV1 /FVC is the most sensitive measure of early or mild airway obstruction in children with cystic fibrosis. If only the FEV1 /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.