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Spirometry Interpretation

Enter observed and predicted FEV₁ and FVC to calculate the FEV₁/FVC ratio, percentages of predicted, and interpret ventilatory pattern.

Results

FEV₁/FVC ratio

75.0%

Observed ratio

Predicted ratio

83.9%

Based on reference values

FEV₁ % predicted

81%

Severity grading for obstruction

FVC % predicted

90%

Consider restriction if <80%

Normal ratio—no obstruction.

Compare to lower limit of normal (LLN) where available for age-adjusted decisions.

How to Use This Calculator

Ensure ATS/ERS acceptability criteria: good start, ≥6-second exhalation, repeatability among maneuvers. Use race-appropriate reference values (GLI if available) for FEV₁ and FVC to gauge severity. Combine ratio with lung volumes, DLCO, and imaging when diagnosing COPD, asthma, or restrictive diseases.

Formula

FEV₁/FVC ratio (%) = (FEV₁ ÷ FVC) × 100.

Frequently Asked Questions

LLN is the 5th percentile of reference population. When available, use LLN instead of fixed 0.70 threshold, especially in older adults. GOLD staging uses FEV₁ % predicted after confirming obstruction (ratio <0.70). Stage 1 ≥80%, Stage 2 50–79%, Stage 3 30–49%, Stage 4 <30%. Yes—between attacks or after bronchodilator therapy. Perform bronchodilator challenge or bronchoprovocation if suspicion persists. Reduced FVC with normal ratio suggests restriction or poor effort; correlate with lung volumes and imaging. Compare pre- and post-bronchodilator values to assess reversibility (>12% and 200 mL improvement in FEV₁ or FVC).