What are the PFT (Pulmonary Function Test) diagnostic criteria for Chronic Obstructive Pulmonary Disease (COPD)?

PFT Diagnostic Criteria for COPD

COPD is diagnosed on pulmonary function testing when post-bronchodilator spirometry demonstrates a FEV1/FVC ratio <0.70, which must be accompanied by appropriate respiratory symptoms (such as dyspnea, chronic cough, or sputum production) and significant exposure history to noxious stimuli (typically >40 pack-years of smoking or equivalent occupational/environmental exposures). 1, 2

Essential Spirometric Requirements

Post-bronchodilator values are mandatory - the diagnosis cannot be made on pre-bronchodilator spirometry alone, as this is a critical pitfall that leads to misdiagnosis. 3, 1 The bronchodilator testing should use either:

• 400 mcg of salbutamol (albuterol), OR
• 80 mcg of ipratropium bromide 3

The post-bronchodilator FEV1/FVC ratio <0.70 confirms persistent airflow limitation that is not fully reversible, which is the hallmark of COPD. 1

Severity Staging After Diagnosis

Once COPD is diagnosed, severity is classified using post-bronchodilator FEV1 % predicted according to GOLD criteria: 1, 2

• GOLD 1 (Mild): FEV1 ≥80% predicted
• GOLD 2 (Moderate): FEV1 50-79% predicted
• GOLD 3 (Severe): FEV1 30-49% predicted
• GOLD 4 (Very Severe): FEV1 <30% predicted

Important Controversy: Fixed Ratio vs. Lower Limit of Normal

While the fixed ratio of 0.70 remains the standard in most clinical guidelines (England, Wales, France, Germany, Finland, Portugal, Russia), 3 there is ongoing debate about its limitations:

• The fixed ratio may overdiagnose COPD in elderly patients (>70 years) and underdiagnose in younger adults (<45-50 years) compared to age-adjusted norms. 1
• Some European guidelines (Czech Republic, Italy, Poland, Sweden) recommend using the lower limit of normal (LLN) - defined as below the 5th percentile for age, sex, and height - particularly for patients <50 years and >70 years. 3
• For epidemiological studies, the European Respiratory Society recommends LLN over the fixed ratio. 3

However, the fixed ratio of 0.70 is simpler to apply, independent of reference values, and remains the most widely used criterion in clinical practice. 1

Critical Diagnostic Pitfalls to Avoid

Spirometry alone is insufficient - you must integrate three components: 1, 2

1. Post-bronchodilator FEV1/FVC <0.70
2. Appropriate respiratory symptoms (progressive dyspnea, chronic cough, sputum production, recurrent respiratory infections)
3. Significant exposure history (smoking, occupational exposures, biomass fuel)

Do not diagnose COPD based on pre-bronchodilator values - this is a common error that significantly affects prevalence estimates and diagnostic accuracy. 3, 1

Rule out alternative diagnoses - particularly asthma and other respiratory diseases must be excluded before confirming COPD. 1 The fixed ratio criteria alone has 100% sensitivity but only 38% specificity for distinguishing COPD from asthma, meaning it will catch all COPD cases but may misclassify asthma patients. 4

Technical Considerations

FEV1/VC (slow vital capacity) is more accurate than FEV1/FVC for identifying obstruction, because FVC is more flow-dependent than slow vital capacity. 1 However, FEV1/FVC remains the standard in most guidelines due to widespread availability and established reference values.

Spirometry must be performed according to ATS/ERS technical standards to ensure accuracy. 3