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Pulmonary Function Tests (PFT)

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Pulmonary Function Tests (PFTs)

Also called

Lung function tests

ICD-10

N/A (Diagnostic Procedure)

Specialty

Pulmonolgy

Onset

For Chronic Conditions

Reviewed

July 2026

On This Page

Overview

Pulmonary Function Tests (PFTs) assess how well the lungs:

  • Move air in and out
  • Exchange oxygen and carbon dioxide
  • Transfer gases across the alveolar-capillary membrane

They are used to:

  • Diagnose lung diseases
  • Assess disease severity
  • Monitor disease progression
  • Evaluate response to treatment

Indications

-Diagnostic

  • Asthma
  • COPD
  • Interstitial lung disease (ILD)
  • Bronchiectasis
  • Occupational lung disease
  • Unexplained dyspnea
  • Chronic cough

–Monitoring

    • Disease progression
    • Response to treatment
    • Preoperative assessment
    • Occupational health screening

Contraindications

    • Do not perform Pulmonary Function Tests (PFTs) in patients with:

      • Recent myocardial infarction (within the previous month)
      • Unstable angina
      • Untreated pneumothorax
      • Massive hemoptysis of unknown cause
      • Recent thoracic, abdominal, or intracranial surgery
      • Recent eye surgery (e.g., cataract or retinal surgery)
      • Thoracic, abdominal, or cerebral aneurysm
      • Active respiratory infection (relative contraindication)
      • Severe respiratory distress or inability to perform the test
      • Inability to cooperate or follow instructions

Types of Pulmonary Function Tests

    1. Spirometry

      Measures:

      • FEV₁

      • FVC

      • FEV₁/FVC ratio

      Mainly assesses airflow limitation.

      Lung Volumes

      Measures:

      • Total lung capacity (TLC)

      • Residual volume (RV)

      • Functional residual capacity (FRC)

      Assesses restrictive lung disease and hyperinflation.

      Diffusing Capacity (DLCO)

      Measures:

      • Gas transfer across the alveolar-capillary membrane

      Reduced in:

      • ILD

      • Emphysema

      • Pulmonary vascular disease

      Peak Expiratory Flow (PEF)

      Measures:

      • Maximum expiratory flow

      Commonly used for:

      • Asthma monitoring

Normal Spirometry Values

FEV₁

  • Forced expiratory volume in the first second

FVC

  • Forced vital capacity

FEV₁/FVC Ratio

    • Normal: ≥0.70 (or above the lower limit of normal)

Interpretation

-Obstructive Pattern

Features:

  • ↓ FEV₁

  • ↓ FEV₁/FVC ratio (<0.70)

  • Normal or increased TLC

Common causes:

  • Asthma

  • COPD

  • Bronchiectasis

-Restrictive Pattern

Features:

  • ↓ FVC

  • ↓ TLC

  • Normal or increased FEV₁/FVC ratio

Common causes:

  • Interstitial lung disease

  • Chest wall disorders

  • Neuromuscular disease

  • Obesity

-Mixed Pattern

Features:

  • ↓ FEV₁/FVC ratio

  • ↓ TLC

Seen in patients with both obstructive and restrictive disease.

Important Note

Spirometry alone cannot confirm restriction—measurement of total lung capacity (TLC) is required.

Bronchodilator Reversibility Testing

    • Performed by:

      • Spirometry before bronchodilator
      • Administration of a short-acting bronchodilator
      • Repeat spirometry after 10–15 minutes

      Significant Bronchodilator Response

      • Increase in FEV₁ or FVC ≥12% and ≥200 mL from baseline

      Suggests:

      • Reversible airflow obstruction (e.g., asthma)

      Important Note

      A positive bronchodilator response supports asthma but does not exclude COPD.

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Related Topics

Complications of Pulmonary Function Tests (PFTs)

    • Pulmonary Function Tests (PFTs)​ are generally safe.

      Rare complications include:

      • Dizziness
      • Cough
      • Bronchospasm
      • Syncope
      • Chest discomfort
      • Pneumothorax (very rare)

Prognosis of Pulmonary Function Tests (PFTs)

    • Pulmonary Function Tests (PFTs)​ do not determine prognosis directly but provide valuable information about:

      • Disease severity
      • Functional impairment
      • Response to therapy
      • Disease progression

    Serial PFTs help monitor long-term outcomes in chronic respiratory diseases.

Key Points / Clinical Pearls of Pulmonary Function Tests (PFTs)

    • PFTs are noninvasive tests used to assess lung function.
    • Spirometry is the most commonly performed pulmonary function test.
    • FEV₁/FVC ratio is reduced in obstructive lung disease.
    • Restriction requires confirmation with a reduced TLC.
    • DLCO assesses gas transfer across the alveolar-capillary membrane.
    • Bronchodilator reversibility testing helps identify reversible airflow obstruction.
    • Peak expiratory flow is commonly used to monitor asthma.
    • PFTs should not be performed during acute severe respiratory illness.