Spirometry Interpretation (ATS/ERS 2021)

The Spirometry Interpretation section shows the automatically calculated spirometry pattern, following the ATS/ERS 2021 Technical Standard. This interpretation helps you quickly identify the type and severity of abnormality based on accepted reference thresholds.

When it’s available

  • The spirometry pattern is available only for tests using GLI/Quanjer reference values.

    • It cannot be calculated for Hedenström/Solymar.

  • The same calculation method is applied for all regions.

  • It appears above the spirometry graph and is also included in the automatically generated summary text.

  • Not available for spirometries made prior to May 18 2026

How the interpretation is calculated

The calculation is based on FEV₁, FVC, and FEV₁/FVC values compared with the Lower Limit of Normal (LLN), defined as the 5th percentile of the reference population.

Normal (Within expected range)

  • Lung function is higher than the LLN.

Obstructive pattern

  • FEV₁/FVC is below the LLN (5th percentile).

Restrictive pattern

  • FVC is below the LLN (5th percentile).

    • Note: The ATS/ERS 2021 standard defines restriction using TLC < 5th percentile. Since total lung capacity (TLC) is not available in this spirometry tool, FVC is used as a proxy measure.

Mixed pattern

  • FEV₁/FVC and FVC are both below the LLN (5th percentile).

Severity grading

Severity is determined using the Z-score of the relevant parameter(s) for each identified pattern:

Pattern Parameter(s) used for severity Z-score ranges
Obstructive FEV₁ Mild: -1.65 to -2.5
Moderate: -2.51 to -4.0
Severe: < -4.1
Restrictive FVC Mild: -1.65 to -2.5
Moderate: -2.51 to -4.0
Severe: < -4.1
Mixed FEV₁ and FVC (lowest Z-score determines severity) Same thresholds as above
Normal Within expected range —

This ensures that severity reflects the most relevant physiological limitation for each pattern type.

Possible outcomes

The spirometry interpretation can display one of the following:

  • Normal

  • Mild / Moderate / Severe Obstruction

  • Mild / Moderate / Severe Restriction

  • Mixed pattern

When interpretation is not available, the display will indicate:

  • “Not available for the selected reference values,” or

  • “Not available for tests made prior to [release date].”

Was this article helpful?

    Got a second? Tell us more about what you think





    Thanks for helping us improve!

    Have more questions? Contact support

    Related articles

    Spirometry & Bronchodilator Test — Quick Guide Spirometry & Bronchodilator Test — What patients see Spirometry Quality Grading Bronchodilator Response (ATS/ERS 2005 & 2021) Z-score for spirometries