To assess the sensitivity, specificity, positive and negative predictive values of greater than 12% improvement in FEV1, or greater than 25% improvement in FEF25-75 as predictors of a positive methacholine challenge in patients with a suspected diagnosis of asthma.
378 patients, 158 females and 220 males, with a suspected diagnosis of asthma underwent pulmonary function testing pre and post bronchodilator administration and a methacholine challenge. Sensitivity, specificity, positive and negative predictive values for FEV1, FEF25-75, and either parameter were calculated. Youden Index was also calculated to assess the overall best test.
For FEV1, the sensitivity and specificity in predicting a positive methacholine challenge where 42.2% and 79.9% respectively [positive (PPV) and negative predictive values (NPV), 39.6% and 18.4% respectively]. For FEF25-75, the sensitivity and specificity in predicting a positive methacholine challenge where 26.8% and 89.2% respectively (PPV and NPV, 43.7% and 20.4% respectively). When using either FEV1 or FEF25-75, the sensitivity and specificity in predicting a positive methacholine challenge where 47.8% and 78.8% respectively (PPV and NPV, 41.4% and 17%, respectively). The Youden Index for FEV1 was 22%, for FEF25-75 was 15.9%, and for either FEV1 or FEF25-75 was 26.7%.
FEV1 is a more sensitive test in predicting a positive methacholine test whereas FEF25-75 is a more specific test. The use of either criterion improved sensitivity at a small cost in specificity. Based on the Youden Index either criterion is the best over all test.
Neither FEV1 nor FEF25-75 are good predictors of a positive methacholine challenge. The application of either test does not improve this predictibility. In patients with suspected asthma and negative bronchodilator response methacholine challenge should still be performed to assess the presence of underlying hyperreactive airways disease.
Table 1Total Number of Patients378Males (%) / Females (%)220 (58.2%) / 158 (41.8%)Age [Mean (Range)]44.5 (16-71)FEV1 > 12% [Number (%)]96 (25.4%)FEF25-75 > 25% [Number (%)]55 (14.6%)Positive Methacholine [Number (%)]90 (23.8%)
Zoheir Bshouty, None.