If the FEV1/FVC ratio is less that 80%, the next question spirometry can answer is the severity of the obstructive defect. To do this, look at the FEV1 percent predicted:
> 80% = minimal obstructive defect
65 - 80% = mild obstructive defect
50 - 65% = moderate obstructive defect
< 50% = severe obstructive defect