Ans. c (15%) (Ref. H - 18th/pg. ch. 254)The diagnosis of asthma is established by demonstrating reversible airway obstruction. Reversibility is traditionally defined as a = 15% increase in FEV1 after two puffs of a ss-adrenergic agonist.THE DIAGNOSIS OF ASTHMA# When the spirometry results are normal at presentation; diagnosis can be made by showing heightened airway responsiveness to challenges with histamine, methacholine, isocapnic hyperventilation of cold air.# Once the diagnosis is confirmed, the course of the illness and the effectiveness of therapy can be followed by measuring PEFRs at home and/or the FEV1 in the office or laboratory.# Positive wheal-and-flare reactions to skin tests can be demonstrated to various allergens, but such findings do not necessarily correlate with the intrapulmonary events. Sputum and blood eosinophilia and measurement of serum IgE levels are also helpful but are not specific for asthma.# Chest roentgenograms showing hyperinflation are also nondiagnostic.