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Summary of criteria for diagnosing obstructive lung disease

A grading system of airway obstructionExpiratory airway obstruction FEV1%(F)VC (corrected for age and sex)
No obstruction * above 5th percentile, and no bronchodilator response
Mild obstruction * below 5th percentile and FEV1%pred >60% , or
above 5th percentile and bronchodilator response
Moderate obstruction * below 5th percentile and FEV1%pred 40-59%
Severe obstruction * below 5th percentile and FEV1%pred <40%

Bronchodilator responseBronchodilator response Criteria for grading of response
No response Increase in FEV1 < 200 mL and < 9% initial FEV1
Mild response Increase in FEV1 > 200 mL and/or > 9% initial FEV1
Marked response Increase in FEV1 > 12% initial FEV1 and > 200 mL
Possibly response According to FEV1 no bronchodilator responsiveness, but increase in (F)VC > 340 mL and/or > 12% initial value and fall in FEV1%(F)VC < 2%: the increase in (F)VC might reflect better subject cooperation

Reversibility of airway obstruction  
No reversibility Airway obstruction but no response to bronchilator drug
Partial reversibility In spite of the response to a bronchodilator drug the FEV1%(F)VC is still below the 5th percentile
Completely reversible FEV1%(F)VC after the bronchodilator drug is above the 5th percentile

Criteria for a VC that is too smallVC too low Criterion
Moderate below 5th percentile but z-score > -3
Severe z-score < -3.0

FEV1 Criterion
Too low below 5th percentile

* There is no uniformity in recommendations. The criteria shown comply with the BTS 1997 recommendation, which has since been superseded.

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