Methacholine and histamine inhalation challenges in asthma: relationships to age of onset, length of illness, and pulmonary functions.

Levels of airways hyperreactivity, as indexed by methacholine and histamine thresholds, were determined for hospitalized asthmatic patients using the serial concentration, constant-breath method. Airways hyperreactivity was categorized into low and high based on a split of the sample of subjects tested. These categories were unrelated to pulmonary function measurements obtained throughout hospitalization. Patients having high airways hyperreactivity to histamine or methacholine were admitted for intensive inpatient care at a young age, had an earlier age of onset, and had asthma of longer duration than patients having low airways hyperreactivity. These latter results suggested that relatively greater airways hyperreacticity is more likely to be associated with early onset of the illness.