Reference — Pulmonary Function Testing
PFT Interpretation Reference
A bedside lookup for reading pulmonary function tests — the obstruction and restriction defining patterns, the FEV₁ percent-predicted severity bands, the bronchodilator reversibility criteria, and the DLCO grading — in one scannable reference.
Written by Apex Respiratory Editorial Team
Educational use only. This material supports respiratory therapy education and exam review. It is not medical advice and is not a substitute for clinical judgment, institutional protocols, or physician orders. Always follow facility policies and current provider orders, and verify calculations independently before clinical use.
Overview
The numeric cutoffs that turn PFT values into an interpretation, in one place. Use them with the patient’s predicted values (reference equations by age, sex, height, and ethnicity) and the clinical picture; published thresholds vary slightly by guideline.
Defining Patterns
| Pattern | Hallmark |
|---|---|
| Obstruction | FEV₁/FVC reduced (below 0.70 fixed, or below the LLN). |
| Restriction | TLC reduced (below 80% predicted or below the LLN), with a normal or high FEV₁/FVC. |
| Mixed | FEV₁/FVC reduced AND TLC reduced. |
Severity by FEV₁ Percent Predicted (ATS/ERS 2005)
| Severity | FEV₁ % Predicted |
|---|---|
| Mild | 70% or above |
| Moderate | 60-69% |
| Moderately severe | 50-59% |
| Severe | 35-49% |
| Very severe | below 35% |
COPD Airflow Limitation (GOLD)
Post-bronchodilator FEV₁ % predicted when FEV₁/FVC is below 0.70.
| GOLD Grade | FEV₁ % Predicted |
|---|---|
| GOLD 1 (mild) | 80% or above |
| GOLD 2 (moderate) | 50-79% |
| GOLD 3 (severe) | 30-49% |
| GOLD 4 (very severe) | below 30% |
Key Thresholds
| Test | Threshold |
|---|---|
| Significant bronchodilator response | Increase of at least 12% AND at least 200 mL in FEV₁ or FVC (ATS/ERS 2005); greater than 10% predicted (2022 update). |
| Positive methacholine challenge | Fall in FEV₁ of at least 20% (the PC20). |
| DLCO reduced | Below 80% predicted (or below the LLN); graded mild/moderate/severe similarly to FEV₁. |
| Spirometry repeatability | Top two FVC and top two FEV₁ values within 150 mL. |
Clinical Notes
- The fixed cutoff has age bias. The fixed FEV₁/FVC below 0.70 cutoff over-diagnoses obstruction in the elderly and under-diagnoses it in the young; the lower limit of normal (LLN) is more accurate.
- Spirometry cannot confirm restriction. Spirometry alone cannot confirm restriction — a reduced TLC is required.
- Read against predicted, not absolutes. Always interpret against the patient’s predicted set, not the absolute number.
- Name the grading scheme you use. Severity grades differ between the general ATS/ERS scheme and GOLD (which is COPD-specific) — state which you are using.
Related Resources
Sources
- Kacmarek RM, Stoller JK, Heuer AJ. Egan's Fundamentals of Respiratory Care. 12th ed. Elsevier; 2021. Pulmonary function test interpretation chapters.
- Pellegrino R, Viegi G, Brusasco V, et al. Interpretative strategies for lung function tests. Eur Respir J. 2005;26(5):948-968.