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 FEV₁ and FEF_25‐75 of ⩾ 80% and FEF₅₀ ⩾ 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 PC₂₀ and the change in FEF_25‐75 or FEF₅₀ following salbutamol. There was a negative correlation between the initial FEV₁ (% predicted) and the percent change in FEV₁ following salbutamol (P < 0.01). An increase in FEV₁ of >6% occurred in 7/12 (58.3%) patients with PC₂₀ ⩽ 0.25 mg/mL (Group I); in 7/24 (29.2%) patients with PC₂₀ = 0.26–2.0 mg/mL (Group II); in only 1/14 (7.1%) patients with PC₂₀ > 2.1 mg/mL (Group III) and in none of those asymptomatic (control) children with PC₂₀ > 8.0 mg/mL (Group IV). All subjects who had a change in FEV₁ > 6% after salbutamol had a PC₂₀ < 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 FEV₁ a change of > 6% following salbutamol inhalation is indicative of bronchial hyperreactivity. Pediatr Pulmonol 1991; 10:244–248.