Relationship between response to inhaled salbutamol and methacholine bronchial provocation in children with suspected asthma

Fifty children (27 females, 23 males) ages 6–15 years who were referred for evaluation of suspected asthma had baseline FEV 1 and FEF 25‐75 of ⩾ 80% and FEF 50 ⩾ 70% of predicted values. All had these tests repeated on the same day, after inhaling salbutamol. On a subsequent day PC‐20 (methacholine) was determined as an index of bronchial hyperreactivity (BH). Fourteen age‐matched healthy children (6 females, 8 males) were studied in a similar manner. There was no significant relationship between the PC 20 and the change in FEF 25‐75 or FEF 50 following salbutamol. There was a negative correlation between the initial FEV 1 (% predicted) and the percent change in FEV 1 following salbutamol ( P < 0.01). An increase in FEV 1 of >6% occurred in 7/12 (58.3%) patients with PC 20 ⩽ 0.25 mg/mL (Group I); in 7/24 (29.2%) patients with PC 20 = 0.26–2.0 mg/mL (Group II); in only 1/14 (7.1%) patients with PC 20 > 2.1 mg/mL (Group III) and in none of those asymptomatic (control) children with PC 20 > 8.0 mg/mL (Group IV). All subjects who had a change in FEV 1 > 6% after salbutamol had a PC 20 < 8 mg/mL and this test detected the majority of patients with severe BH. However, although the sensitivity of the test was 100%, the predictive value was only 36%. We conclude that in the presence of a normal baseline FEV 1 a change of > 6% following salbutamol inhalation is indicative of bronchial hyperreactivity. Pediatr Pulmonol 1991; 10:244–248.