A positive methacholine challenge test in the absence of symptoms.

A 20-year-old white female nonsmoker presented to the pulmonary function laboratory for a methacholine challenge test. The patient denied wheezing, dyspnea, cough, or chest tightness. In fact, she competes in collegiate basketball and softball without respiratory complaints. She stated that her primary care physician wanted to “screen her for asthma,” because her father is asthmatic. Her medical history was remarkable only for allergic rhinitis. She denied recent or active chest infections. Table 1 shows her baseline spirometry values. She had a substantial bronchospastic response to methacholine inhalation; the provocation concentration (PC20) that caused a 20% decline in forced expiratory volume in the first second (FEV1) was 3.95 mg/mL.