[Pulmonary function testing in asthma].

Spirometry with bronchodilator test is the most frequently used test for asthma diagnosis.  PEF variability can prove variable airflow obstruction when asthma was not confirmed by spirometry with bronchodilator test. Bronchial challenge tests can demonstrate airway hyperresponsiveness.  Measuring exhaled nitric oxide received increased support in the recent asthma diagnosis guidelines. Peripheral airways involvement is common in asthma, can occur despite normal spirometry and be identified by oscillometry and nitrogen gas washout. It is important to continue investigation even if a certain diagnostic test shows negative results when the clinical asthma suspicion persists.