Interpreting Spirometry Results in Primary Care

by

Dr Zaid Ismail

Spirometry is essential in diagnosing and monitoring chronic respiratory conditions like asthma and COPD. Accurate interpretation hinges on understanding the key parameters and patterns.

Key Spirometry Values

  • FEV₁ (Forced Expiratory Volume in 1 second): Volume exhaled in the first second.
  • FVC (Forced Vital Capacity): Total volume exhaled during the forced manoeuvre.
  • FEV₁/FVC ratio: Used to distinguish obstructive from restrictive patterns.

Spirometry Interpretation Summary

PatternFEV₁FVCFEV₁/FVCTypical CausesNext Steps
Obstructive↓Normal or ↓< 0.7Asthma, COPD, BronchiectasisConsider reversibility test
Restrictive↓↓Normal or ↑ILD, obesity, neuromuscular diseaseRefer for full lung function (TLC) testing
Mixed↓↓< 0.7Combined obstructive & restrictive diseaseSpecialist referral recommended
NormalNormalNormal≥ 0.7–If symptomatic, consider alt diagnoses

Obstructive Pattern

  • FEV₁/FVC ratio < 0.7 (post-bronchodilator)
  • Reduced FEV₁, normal or reduced FVC
  • Seen in asthma, COPD, bronchiectasis

Reversibility testing helps differentiate:

  • ≥12% and ≥200 mL improvement in FEV₁ suggests asthma (NICE NG80).
  • Little or no reversibility suggests COPD (GOLD guidelines).

Restrictive Pattern

  • FEV₁/FVC ratio normal or high
  • Reduced FVC
  • Confirmed with reduced Total Lung Capacity (TLC) on full lung function testing
  • Suggests interstitial lung disease, neuromuscular disorders, or chest wall abnormalities

Mixed Pattern

  • Features of both obstruction and restriction
  • Requires full lung function testing and often specialist input

When to Refer

  • Suspected restrictive disease
  • Diagnostic uncertainty (e.g. mixed patterns)
  • Abnormal results with preserved FEV₁/FVC but symptoms persist

Accurate spirometry interpretation supports timely diagnosis and appropriate management. Use a structured approach, ensure quality assurance, and interpret in the clinical context.

References:

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