Read a PFT like the 2022 standard.
PFT interpretation per ERS/ATS 2022: z-scores and LLN, GLI Global, quality grades, obstruction versus GOLD 0.70, TLC for restriction, PRISm, the new bronchodilator rule, DLCO patterns and loops.
Reviewed October 2026 · verify against current guidelines
Have a report in hand — enter the printed z-scores or LLNs in the PFT interpreter. It runs this page's stepwise read, grades severity by z-score, applies the 2022 bronchodilator rule and names the next test. Scope: adult PFTs per the ERS/ATS 2022 interpretive standard, the ATS 2023 race statement, GOLD 2026 and the 2026 GOLD/GLI joint statement. A pattern is physiology, not a diagnosis.
PFT interpretation · 1 of 6
Grade the test before the number.
Why it comes first
Every interpretation assumes a maximal, repeatable effort. The 2019 ATS/ERS spirometry standard grades FEV1 and FVC separately, for the pre- and post-bronchodilator sets separately. Find the grade on the report before you read a single z-score.
Quality grades, adults and children over 6 (ATS/ERS 2019)
| A | Three or more acceptable blows; the two largest values agree within 150 mL. |
|---|---|
| B | Two acceptable blows within 150 mL. |
| C | Two or more acceptable blows within 200 mL. |
| D | Two or more acceptable blows within 250 mL. |
| E | Acceptable blows more than 250 mL apart, or only one acceptable blow. |
| U | No acceptable blow, but at least one usable. |
| F | Nothing acceptable or usable. Do not interpret; repeat the test. |
What makes a blow acceptable (ATS/ERS 2019)
- Back-extrapolated volume no more than 5% of FVC or 100 mL, whichever is greater: a sharp start.
- No cough in the first second (spoils FEV1). No glottic closure in the first second (spoils both FEV1 and FVC) or later in the blow (spoils FVC).
- A real end of exhalation: a plateau (no more than 25 mL in the last second), 15 seconds of exhalation, or an FVC that matches or beats the best prior blow.
- No leak or obstructed mouthpiece.
- Below grade A? Still often useful, but judgment weighs more. ERS/ATS 2022: repeat a poor-quality test before an important decision rests on it.
PFT interpretation · 2 of 6
Normal is a range, not 80%.
LLN and z-scores
The lower limit of normal (LLN) is the 5th percentile of a healthy reference population, a z-score of −1.645. ERS/ATS 2022 strongly discourages the old fixed cutoffs (80% predicted for FEV1, 0.70 for FEV1/FVC) because percent predicted ignores how variability changes with age. By design, about 5% of healthy people fall below the LLN; for two-sided limits (lung volumes, DLCO) false positives approach 10% (ERS/ATS 2022).
Why percent predicted misleads (ERS/ATS 2022, Figure 3)
| Age 22 | For a man of median height, the FEV1 LLN sits at about 81% predicted. |
|---|---|
| Age 85 | For a man of the same height, it sits at about 68% predicted. |
| Same 1.0 L | An FEV1 of 1.0 L gives a z-score of −6.8 in one man and −3.2 in the other. A single percent cutoff cannot be right for both. |
Severity of impairment by z-score (ERS/ATS 2022)
| Normal | z-score above −1.645. |
|---|---|
| Mild | z-score −1.65 to −2.5. |
| Moderate | z-score −2.51 to −4.0. |
| Severe | The standard (text and Table 1) says z-score below −4.1, which leaves a gap after −4.0. We grade values between −4.0 and −4.1 as severe, the safer side. |
Near the line — the ATS 2023 statement: results at or near the LLN must be read cautiously and backed by history, imaging and other tests. A normal result does not exclude disease, and severity of impairment is not severity of disease (ERS/ATS 2022). Weigh the pretest probability, as with any test: see likelihood ratios.
LLN lower limit of normal (5th percentile)z-score standard deviations from the predicted meanFEV1 forced expiratory volume in 1 secondFVC forced vital capacityGLI Global Lung Function InitiativeGOLD Global Initiative for Chronic Obstructive Lung DiseaseBDR bronchodilator responsePEF peak expiratory flow
PFT interpretation · 3 of 6
One equation set, stated on the report.
GLI Global and the ATS 2023 statement
The ATS 2023 statement recommends replacing race- and ethnicity-specific equations with a race-neutral average equation, and names GLI Global (Bowerman, 2023) as one. It also says race and ethnicity adjustment factors should not be used for lung volumes or DLCO. GOLD 2026 describes GLI Global as now the only reference equations officially endorsed by ATS and ERS, and the 2026 GOLD/GLI joint statement agrees they are currently the most appropriate.
Know the limits
- GLI Global is a weighted average of the original GLI groups; ATS 2023 calls it a race composite, not truly race-agnostic, and many populations are still missing.
- GLI Global fits about as well as the GLI 2012 'Other' equation and has wider limits of normal (Bowerman, 2023).
- The GLI DLCO and lung-volume equations come mainly from people of European ancestry, so spirometry and DLCO or volume results can disagree; ATS 2023 asks for extra attention when they do.
- Switching equations changes some occupational and disability classifications (GOLD 2026). The report must state which equations were used.
Why tools cannot just compute it — GLI uses the LMS method: predicted value, spread and skew each carry an age-dependent spline term read from published look-up tables (Quanjer, 2012). Use the z-score and LLN your lab software prints rather than a hand-rolled formula.
PFT interpretation · 4 of 6
Ratio first: obstruction and the 0.70 question.
Obstruction
| Define | FEV1/FVC below the LLN (ERS/ATS 2022). |
|---|---|
| Grade | By the FEV1 z-score on the severity scale (the scale was built from FEV1 cutoffs). A ratio below the LLN with a normal FEV1 has no severity label on that scale (Bhatt, ERJ 2024); read it in context. |
| Dysanapsis | A low ratio from airways that are small relative to the lungs, often with a high FVC. It may be a normal variant or a marker of obstructive risk; pretest probability decides (ERS/ATS 2022). |
| Look | A concave (scooped) expiratory limb on the flow-volume loop is thought to reflect small-airway dysfunction (ERS/ATS 2022). |
Why GOLD still uses 0.70 for COPD
| GOLD 2026 | Post-bronchodilator FEV1/FVC below 0.70 confirms COPD in the right clinical context. It is simple, independent of reference values and is the criterion behind the trials. |
|---|---|
| Where they split | The fixed ratio may overdiagnose COPD in older adults and underdiagnose about 1% of young adults compared with the LLN (GOLD 2026). |
| 2026 joint statement | GOLD and GLI agree the LLN identifies obstruction across populations, but in a symptomatic patient with a suggestive history and exposure, use the fixed ratio to confirm COPD. Spirometry is one measurement inside the clinical picture, not the diagnosis by itself. |
| Near 0.70 | If the post-bronchodilator ratio is between 0.60 and 0.80, confirm with repeat spirometry on another occasion; below 0.60 it is very unlikely to rise above 0.70 (GOLD 2026). |
| COPD staging | GOLD stages airflow obstruction in COPD on the post-bronchodilator FEV1 % predicted (GLI Global), not on the z-score (GOLD 2026). Report both when COPD is the question; the COPD tool applies the GOLD grade. |
| Pre vs post | GOLD 2026: pre-bronchodilator spirometry without obstruction can exclude COPD unless suspicion is very high; confirm an obstructed result with post-bronchodilator values. Obstructed before but not after bronchodilator: higher risk of later COPD, so follow closely. |
Bronchodilator response, 2022 definition
| Rule | A rise of more than 10% of the predicted value in FEV1 or FVC: (post − pre) ÷ predicted × 100 (ERS/ATS 2022). |
|---|---|
| Worked example | Man, 50, 170 cm: FEV1 2.0 L before, 2.4 L after; predicted 3.32 L. The paper reports a 12.1% rise: significant. By our arithmetic, 0.4 ÷ 3.32 is 12.0%, still significant. |
| Retired rule | The 2005 rule (12% and 200 mL from baseline) is no longer recommended: it depends on baseline function, height, age and sex. |
| Not a diagnosis | The size of the response varies over time and does not separate COPD from asthma (GOLD 2026). |
Upper (central) airway obstruction on the loop (ERS/ATS 2022)
| Variable extrathoracic | Flattened inspiratory limb; expiration relatively normal. |
|---|---|
| Variable intrathoracic | Flattened expiratory limb; inspiration relatively normal. |
| Fixed | Both limbs flattened. |
| Clue | FEV1 (mL) divided by PEF (L/min) above 8 suggests central or upper airway obstruction; poor initial effort also raises it. |
| Pitfall | Normal spirometry does not rule out central airway disease (ERS/ATS 2022). Stridor or a flattened limb needs direct airway evaluation. After a COPD diagnosis, see AECOPD and the COPD tool. |
PFT interpretation · 5 of 6
Restriction needs a TLC.
Patterns once the ratio is normal (ERS/ATS 2022)
| Restriction | TLC below the LLN. A low FVC alone does not prove it; a normal FVC usually excludes it (Table 8). Extrapulmonary causes include weakness, chest wall disease and obesity (Table 4). |
|---|---|
| Non-specific | Low FEV1 and/or FVC, normal ratio, normal TLC. Causes include submaximal effort, early restriction and early small-airway disease. |
| PRISm | The same spirometry with no TLC measured. ERS/ATS 2022 uses the term for current and former smokers in population studies; GOLD 2026 defines it as post-bronchodilator ratio of 0.70 or more with FEV1 below 80% of reference. |
| Mixed | FEV1/FVC and TLC both below the LLN. |
| Isolated low FEV1 | Normal FVC and ratio: non-specific (PRISm in GOLD terms if post-bronchodilator FEV1 is below 80%). With a normal FVC, restriction is unlikely. |
Traps
- In obstruction, a low FVC may be air trapping (a raised RV), but superimposed restriction cannot be ruled out without TLC (ERS/ATS 2022).
- Single-breath VA and multi-breath dilution underestimate TLC in obstruction, by as much as 3 L when severe; a low value with a low ratio does not make a mixed defect. Plethysmography can overestimate volume in severe obstruction (ERS/ATS 2022).
- A low single-breath VA on its own only suggests restriction; confirm with plethysmography or multi-breath dilution (ERS/ATS 2022, Table 8).
- An SVC more than 100 mL above the FVC suggests airway collapse during forced exhalation (ERS/ATS 2022).
- PRISm is unstable: about 20% to 30% move to obstruction over time, and it carries higher cardiopulmonary and mortality risk (GOLD 2026).
Next test — for a non-specific pattern or possible restriction, measure TLC, and repeat after bronchodilator if effort was maximal. ERS/ATS 2022 (p. 16): restriction presenting as the non-specific pattern is often a chest wall or neuromuscular disorder, so respiratory muscle strength and DLCO are reasonable next steps (our suggestion).
TLC total lung capacityRV residual volumeVA alveolar volumePRISm preserved ratio impaired spirometryVC vital capacity
PFT interpretation · 6 of 6
DLCO, then the stepwise read.
Correct for hemoglobin first
ERS/ATS 2022: adjust the DLCO reference for the measured hemoglobin, especially when tracking drug toxicity. The GLI DLCO equations were built on data uncorrected for hemoglobin (Stanojevic, 2017). The ERS/ATS 2017 standard (equations 31 and 32, derived from its eq. 3 with DM/θVc taken as 0.7) multiplies predicted DLCO by 1.7 × Hb ÷ (10.22 + Hb) in males 15 and older, and by 1.7 × Hb ÷ (9.38 + Hb) in females and children under 15, with Hb in g/dL. Anemia lowers DLCO; erythrocytosis raises it.
Reading a DLCO (ERS/ATS 2022)
| Low, VA normal | Pulmonary vascular abnormality (pulmonary hypertension, embolism, vasculitis), emphysema with preserved volume, early ILD, or anemia. |
|---|---|
| Low, VA low, KCO low or normal | Loss of alveolar-capillary units: emphysema, or ILD with lost volume. A normal KCO with a low VA is not reassuring: KCO rises as volume falls, so it cannot correct for the low VA. |
| Low, VA low, KCO high | A low-volume state: incomplete expansion (failure to take a deep breath, neuromuscular dysfunction) or resection. |
| Low, VA low, KCO unknown | Get the KCO (with its upper limit or z-score) before choosing a branch: normal versus high KCO is the fork. |
| High | Increased pulmonary blood flow (left-to-right shunt, asthma, obesity), erythrocytosis, or alveolar hemorrhage. |
Putting it together (our reading of Figure 11) — with obstruction, a low DLCO points toward emphysema, which sits in both low-DLCO branches. A low VA with a high KCO is a low-volume state: check effort and respiratory muscle strength, ask about resection, and look for extrapulmonary causes first. A low VA with a low or normal KCO is where CT earns its place.
The stepwise read
- Quality. Grade and equation set. Grade F: stop and repeat.
- Ratio. FEV1/FVC below the LLN? Obstruction. If COPD is the question, also check the post-bronchodilator ratio against 0.70.
- FVC and FEV1. With a normal ratio, are either below the LLN? Then it is non-specific or restrictive until TLC answers.
- TLC. Below the LLN: restriction, or mixed if the ratio is also low. Not measured: say so, and do not call restriction.
- Severity. ERS/ATS 2022 grades all measures by z-score. Grading obstruction on FEV1 follows how the scale was built; grading restriction on the TLC z-score is a convention, not a rule. For COPD, also give GOLD's post-bronchodilator FEV1 % predicted.
- Bronchodilator. Rise more than 10% of predicted in FEV1 or FVC.
- DLCO. Hemoglobin-adjusted; then read it with VA and the pattern.
- Loop. Concave in small-airway disease; flattened limbs in central obstruction.
- Next test. Name the question the pattern leaves open.
Worked example (illustrative patient)
| Report | Woman, 64, grade A. FEV1/FVC z −2.90. FEV1 z −2.70. FVC z −1.20. TLC not done. DLCO z −2.20, Hb 13.5 g/dL, report already Hb-adjusted. |
|---|---|
| Pattern | Ratio below the LLN: obstruction. The FVC is within normal limits, so there is no low FVC raising the air-trapping versus mixed-defect question. |
| Severity | FEV1 z −2.70: moderate. |
| Bronchodilator | FEV1 1.60 to 1.85 L, predicted 2.90 L: 0.25 ÷ 2.90 = 8.6% of predicted, not significant in 2022 terms (the retired 2005 rule would have called 15.6% and 250 mL a response). |
| DLCO | Low with obstruction: emphysema is the leading candidate (see the note above); VA and KCO, then CT, localise it. |
| COPD staging | GOLD uses post-bronchodilator FEV1 % predicted: 1.85 ÷ 2.90 = 64% here, if 2.90 L is the GLI Global predicted value. |
| GOLD | Post-bronchodilator ratio 0.62: below 0.70 but between 0.60 and 0.80, so GOLD 2026 advises confirming on a repeat test. |
| Next | CT chest if emphysema would change management. Lung volumes only if the FVC falls or the picture changes. |
DLCO diffusing capacity for carbon monoxideKCO transfer coefficient (DLCO ÷ VA)ILD interstitial lung diseaseHb hemoglobin
Educational reference only — not medical advice. Verify against your laboratory's report, current ERS/ATS and GOLD documents, and local protocol.
Sources
Verify against current guidelines and local protocol before acting.
- Stanojevic S, Kaminsky DA, Miller MR, et al. ERS/ATS technical standard on interpretive strategies for routine lung function tests. Eur Respir J 2022;60(1):2101499. doi:10.1183/13993003.01499-2021.
- Bhakta NR, Bime C, Kaminsky DA, et al. Race and ethnicity in pulmonary function test interpretation: an official American Thoracic Society statement. Am J Respir Crit Care Med 2023;207(8):978-995. doi:10.1164/rccm.202302-0310ST.
- Bowerman C, Bhakta NR, Brazzale D, et al. A race-neutral approach to the interpretation of lung function measurements. Am J Respir Crit Care Med 2023;207(6):768-774. doi:10.1164/rccm.202205-0963OC.
- Graham BL, Steenbruggen I, Miller MR, et al. Standardization of spirometry 2019 update: an official ATS and ERS technical statement. Am J Respir Crit Care Med 2019;200(8):e70-e88. doi:10.1164/rccm.201908-1590ST.
- Global Initiative for Chronic Obstructive Lung Disease. GOLD 2026 Report (v1.3, 8 December 2025), Chapter 2: spirometric criteria, PRISm, reference equations (pp. 29-30).
- Halpin DMG, Stanojevic S, McCormack MC, et al. Joint statement from GOLD/GLI regarding the use of spirometry to define airflow obstruction and diagnose COPD. Eur Respir J 2026;67(4):2502574. doi:10.1183/13993003.02574-2025.
- Singh D, Stockley R, Anzueto A, et al. GOLD Science Committee recommendations for the use of pre- and post-bronchodilator spirometry for the diagnosis of COPD. Eur Respir J 2025;65(2):2401603. doi:10.1183/13993003.01603-2024.
- Bhatt SP, Bodduluri S, Nakhmani A. ERS/ATS spirometry interpretation standards: a gap in grading severity of airflow obstruction. Eur Respir J 2024;63(2):2301910. doi:10.1183/13993003.01910-2023.
- Quanjer PH, Stanojevic S, Cole TJ, et al. Multi-ethnic reference values for spirometry for the 3-95-yr age range: the Global Lung Function 2012 equations. Eur Respir J 2012;40(6):1324-1343. doi:10.1183/09031936.00080312.
- Stanojevic S, Graham BL, Cooper BG, et al. Official ERS technical standards: Global Lung Function Initiative reference values for the carbon monoxide transfer factor for Caucasians. Eur Respir J 2017;50(3):1700010. doi:10.1183/13993003.00010-2017.
- Hall GL, et al. Official ERS technical standard: Global Lung Function Initiative reference values for static lung volumes in individuals of European ancestry. Eur Respir J 2021;57(3):2000289. doi:10.1183/13993003.00289-2020.
- Graham BL, Brusasco V, Burgos F, et al. 2017 ERS/ATS standards for single-breath carbon monoxide uptake in the lung. Eur Respir J 2017;49(1):1600016. doi:10.1183/13993003.00016-2016. Hemoglobin adjustment: equations 31-32, derived from eq. 3 with DM/θVc 0.7, p. 23.
- Facts restated in our own words; no society tables or figures reproduced. Not affiliated with or endorsed by ATS, ERS, GLI or GOLD.