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Pulmonology · Interpreter

PFT interpreter

Enter the z-scores or LLNs exactly as your lab printed them. Get the ERS/ATS 2022 pattern, z-score severity, the 2022 bronchodilator rule, a DLCO read with hemoglobin adjustment, the GOLD 0.70 check and the next test.

ERS/ATS 2022 z-scoresBDR over 10% of predictedGLI GlobalReviewed Oct 2026

1Report

Enter each value exactly as printed. This tool does not compute GLI predicted values (see “Why no predicted values” below).

2Spirometry baseline (pre-bronchodilator)

z-scores are negative below the predicted mean. “Value + LLN” works in litres or in % predicted, as long as both numbers use the same unit.

3Lung volume and DLCO

Leave TLC blank if lung volumes were not measured.

Hemoglobin optional

Adults. The Hb constant for males applies from age 15; females and children under 15 share the other constant.

4Bronchodilator optional

Both % predicted values must come from the same predicted value, as on a single report.

5Flow–volume loop optional

How it works

The stepwise read (ERS/ATS 2022)

1. Quality. Grades A–F and U are assigned to FEV1 and FVC separately (ATS/ERS 2019). Grade F has nothing acceptable or usable: repeat, do not interpret. Below A, judgment weighs more.

2. Ratio. FEV1/FVC below the LLN (z below −1.645) = obstruction.

3. TLC. Restriction needs TLC below the LLN. Ratio and TLC both low = mixed. A low FVC or FEV1 with a normal ratio and normal TLC = non-specific pattern; with no TLC measured it stays “possible restriction”, called PRISm in population studies of smokers. An isolated low FEV1 with a normal FVC is non-specific too: a normal FVC usually excludes restriction (Table 8).

TLC method. Plethysmography is trusted in every pattern. Gas dilution (multi-breath) and single-breath VA underestimate TLC in obstruction, so a low value with a low ratio does not establish a mixed defect. A low single-breath VA alone only suggests restriction; confirm with plethysmography or multi-breath dilution (ERS/ATS 2022, Table 8). If the method is not stated, the tool says so before calling restriction or mixed.

4. Severity. ERS/ATS 2022 says to grade all measures by z-score: mild −1.65 to −2.5, moderate −2.51 to −4.0, severe below −4.1 (text and Table 1). Values between −4.0 and −4.1 fall in that gap and are graded severe here (safer side). Grading obstruction on FEV1 follows the standard's origin of the scale; grading restriction on the TLC z-score is our convention. For COPD staging, GOLD uses post-bronchodilator FEV1 % predicted (GLI Global) instead; see the COPD tool.

5. Bronchodilator. Significant when FEV1 or FVC rises by more than 10% of the predicted value: (post − pre) ÷ predicted × 100. From two % predicted values on the same report it is simply post % − pre %.

6. DLCO. Read with the hemoglobin, VA and the pattern.

Each value is rounded to the precision shown (z to 2 decimals, BDR to 0.1%) before it is classified. Blank means not measured, never normal.

Why no predicted values

GLI equations (2012 spirometry, 2017 DLCO, 2021 lung volumes, 2022 GLI Global) use the LMS method: the predicted median (M), spread (S) and skew (L) each depend on age through spline terms that are published as look-up tables, interpolated to exact age. A short formula cannot reproduce them, and a near-miss shifts the LLN. Your lab software prints the real z-score and LLN; use those.

For the same reason, % predicted alone cannot be compared with the LLN: the FEV1 LLN is about 81% predicted at age 22 and about 68% at 85 (ERS/ATS 2022). The tool uses % predicted only for the bronchodilator rule and the hemoglobin adjustment.

GOLD 0.70 versus the LLN

GOLD 2026 confirms COPD with a post-bronchodilator FEV1/FVC below 0.70 in a patient with symptoms or exposure. Compared with the LLN, the fixed ratio may overdiagnose older adults and underdiagnose about 1% of young adults. Repeat on another occasion when the post-BD ratio is 0.60–0.80; below 0.60 it is very unlikely to rise above 0.70. The 2026 GOLD/GLI joint statement: in a symptomatic patient with a suggestive history, use the fixed ratio to confirm COPD.

Hemoglobin adjustment and DLCO patterns
Predicted (and LLN) × 1.7·Hb ÷ (10.22 + Hb), males 15 and older · × 1.7·Hb ÷ (9.38 + Hb), females and children · Hb in g/dL

The constants are 0.7 × 14.6 and 0.7 × 13.4 g/dL. ERS/ATS 2017, equations 31–32 (derived from eq. 3 with DM/θVc 0.7). Applied to the LLN when you enter value + LLN, and as % predicted ÷ factor when you enter % predicted. A printed z-score cannot be re-adjusted here. The 2017 standard adjusts predicted DLCO only, so KCO is read as printed (not Hb-adjusted here).

Low DLCO, VA normal: pulmonary vascular disease (pulmonary hypertension, embolism, vasculitis), emphysema with preserved volume, early ILD, anemia. Low VA, KCO low or normal: loss of alveolar–capillary units (emphysema, ILD); a “normal” KCO with a low VA is not reassuring, because KCO rises as volume falls. Low VA, KCO high: incomplete expansion (failure to take a deep breath, neuromuscular dysfunction) or resection. High DLCO: increased pulmonary blood flow (left-to-right shunt, asthma, obesity), erythrocytosis, alveolar hemorrhage (ERS/ATS 2022, Figure 11).

Loops: flat inspiratory limb = variable extrathoracic obstruction; flat expiratory = variable intrathoracic; both = fixed. FEV1 (mL) ÷ PEF (L/min) above 8 suggests central or upper airway obstruction (ERS/ATS 2022).

Sources

  1. Stanojevic S, Kaminsky DA, Miller MR, et al. ERS/ATS technical standard on interpretive strategies for routine lung function tests. Eur Respir J 2022;60:2101499. doi:10.1183/13993003.01499-2021
  2. Bhakta NR, Bime C, Kaminsky DA, et al. Race and ethnicity in pulmonary function test interpretation: an official ATS statement. Am J Respir Crit Care Med 2023;207:978–995.
  3. Bowerman C, Bhakta NR, Brazzale D, et al. A race-neutral approach to the interpretation of lung function measurements (GLI Global). Am J Respir Crit Care Med 2023;207:768–774.
  4. Graham BL, Steenbruggen I, Miller MR, et al. Standardization of spirometry 2019 update (quality grades A–F, U). Am J Respir Crit Care Med 2019;200:e70–e88.
  5. Global Initiative for Chronic Obstructive Lung Disease. GOLD 2026 Report, v1.3 (8 Dec 2025), Chapter 2: spirometric criteria (pp. 29–30) and PRISm.
  6. 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;67:2502574.
  7. Bhatt SP, Bodduluri S, Nakhmani A. ERS/ATS spirometry interpretation standards: a gap in grading severity of airflow obstruction. Eur Respir J 2024;63:2301910.
  8. 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;49:1600016. Hemoglobin adjustment: equations 31–32, derived from eq. 3 with DM/θVc 0.7 (reference Hb 14.6 and 13.4 g/dL).
  9. Quanjer PH, Stanojevic S, Cole TJ, et al. Global Lung Function 2012 equations (LMS method, age spline look-up tables). Eur Respir J 2012;40:1324–1343.

Educational reference only — not a substitute for clinical judgment, institutional protocols, or specialist advice. Calculations run in your browser; nothing you enter is sent or stored.