When interpreting pulmonary function tests, often, not all the criteria are met, and this may limit the reliability of the test if the results are abnormal. If the spirometric results are normal, the test can be interpreted as normal even though all criteria may not be met.

Test acceptability is best determined by examining the flow volume loop and volume time curve. Variable effort, cough, and early glottic closure can be seen on the graphs but may not be apparent by simply looking at values for FEV1 and FVC.