The significance of lung function tests in the differential diagnosis of bronchial asthma.

Measurement of airflow limitation and assessment of its reversibility are essential in estimating the correct diagnosis of asthma. The presence of at least 15% reversibility in FEV1 or PEF after inhalation of a short-acting beta 2-agonist favours the diagnosis, but lack of a short-term reversibility does not exclude asthma. Advanced emphysema, upper airway stenosis and respiratory muscle weakness can, usually, be differentiated from asthma solely by their lung function characteristics. Monitoring of parameters (e.g. PEF) reflecting daily variation of airways' calibre, measurement of bronchial responsiveness to exercise, and to certain bronchospasmogenic mediators, non-isosmolar solutions may help in the differential diagnosis of asthma in a symptom-free condition. Cutoff values, sensitivity and specificity for asthma of these tests are discussed.