PURPOSE: Forced mid-expiratory flow (FEF25-75%) has been proposed as a more sensitive predictor of a positive response in a methacholine challenge test (MCT). If it is more sensitive than FEV1, patients may still show significant decline in FEF25-75% when MCT is otherwise negative at the highest PC20. The clinical significance of these drops in FEF25-75%, however, is unclear. The purpose of our study is to determine whether these drops in FEF25-75% in an otherwise negative MCT would predict future occurrence of asthma over a three year period.
METHODS: 100 consecutive patients with a negative methacholine challenge test, done between May 2003 and January 2004 in a tertiary care hospital, were analyzed. Two pulmonary fellows, blinded to study patient's MCT results, independently reviewed their electronic medical records a minimum of three years from the date of test. Patients were classified into one of five categories: Asthmatic, Likely Asthmatic, Unclear, Likely Not Asthmatic, and Not Asthmatic. Differences were mutually resolved, and unresolved cases were deferred to a senior staff pulmonologist. Results were analyzed using ANOVA test.
RESULTS: Out of 100 patients, 32 were excluded due to lack of three year follow-up. There was initial agreement as to the diagnosis among the physicians in 48 patients, 15 were grouped with mutual agreement and 5 deferred to senior staff pulmonologist. After complete data review, 8 patients were placed in ‘Asthmatic', 4 in ‘Likely Asthmatic', 8 each in ‘Unclear’ and ‘Likely Not Asthmatic', and 40 in ‘Not Asthmatic’ category. The average drop in FEF25-75% in the groups was 20%, 22%, 23%, 12% and 17% respectively. There was no correlation between the drop in forced mid-expiratory flows and asthma (p=0.19).
CONCLUSION: We found no correlation between the drop in FEF25-75% and future development of asthma after three years.
CLINICAL IMPLICATIONS: This data suggests that MCT reductions in FEF25-75% are of little predictive value for the development of asthma and should be interpreted with caution.
DISCLOSURE: Imran Khalid, No Financial Disclosure Information; No Product/Research Disclosure Information