Pulmonary function testing
Pulmonary function testing uses spirometry, lung volumes, and DLCO to classify abnormal lung physiology as obstructive, restrictive, or mixed and to grade severity against percent-predicted values. A reduced FEV1/FVC ratio defines obstruction, a reduced total lung capacity confirms restriction, and DLCO distinguishes the underlying cause and guides whether bronchodilator or bronchial challenge testing is added.
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What this article covers
- Overview
Definition: pulmonary function testing (PFT) is a battery of standardized measurements, spirometry, lung volumes, diffusing capacity for carbon monoxide (DLCO), and bronchodilator or bronchial…
- Epidemiology
Spirometry is indicated in every patient aged 40 years or older with progressive dyspnea, chronic cough, chronic sputum, or recurrent lower respiratory infections, particularly with smoking history…
- Risk factors
Smoking history, the leading indication for spirometry and the dominant risk factor for an obstructive pattern.
- Pathophysiology
Obstruction reflects increased airway resistance: airway narrowing (bronchospasm, wall inflammation, or loss of elastic recoil in emphysema) slows expiratory airflow disproportionately to volume…
- Clinical features
Testing is prompted by symptoms, not a self-defining presentation: dyspnea, chronic cough, wheeze, or reduced exercise tolerance are the usual triggers; a normal examination does not exclude an abnormal result.
- Differential diagnosis
Asthma: asthma shows a reduced FEV1/FVC ratio that reverses with bronchodilator (up at least 12% and 200 mL); discriminated from COPD by substantial reversibility and, when spirometry is normal, a positive methacholine challenge.
- Diagnosis
PFT interpretation classifies the abnormality as obstructive, restrictive, or mixed and grades severity; there is no single disease "criterion" but a defined algorithm: FEV1/FVC and vital capacity…
- Management
First, order the test that answers the clinical question, since the full algorithm is not run in every patient: spirometry alone for suspected obstruction, add lung volumes when restriction is…
- Complications
Misdiagnosis from a technically inadequate test, when poor effort or premature termination is treated as a true abnormality.
- Prognosis
A percent-predicted value below 80% defines pulmonary impairment, and the severity band tracks with symptom burden and, in COPD, exacerbation risk and mortality.
- Prevention
Screen with spirometry at age 40 years or older with progressive dyspnea, chronic cough, chronic sputum, or recurrent lower respiratory infections, particularly with smoking or occupational history…
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