What components of pulmonary function tests (PFTs) should be ordered for a patient with a history of smoking and suspected chronic bronchitis?

Pulmonary Function Testing for Suspected Chronic Bronchitis

For a patient with smoking history and suspected chronic bronchitis, order spirometry with bronchodilator testing, static lung volumes (TLC, FRC, RV), and diffusing capacity for carbon monoxide (DLCO). 1, 2

Essential PFT Components

Spirometry with Bronchodilator Testing (Mandatory)

• Spirometry is the cornerstone diagnostic test and must be performed to establish the diagnosis of chronic bronchitis and COPD 2, 3
• Post-bronchodilator spirometry (after 400 mcg albuterol or equivalent) is required to document the degree and reversibility of airflow obstruction 2, 4
• Key measurements include:
  • FEV1/FVC ratio <0.70 confirms persistent airflow limitation and establishes COPD diagnosis 2, 4
  • FEV1 percentage predicted determines severity classification 5, 2
  • Bronchodilator response ≥12% and ≥200 mL improvement in FEV1 suggests reversible component 6

Static Lung Volumes (Strongly Recommended)

• Measure TLC, FRC, and RV to distinguish chronic bronchitis from emphysema and assess hyperinflation 5, 7
• In chronic bronchitis with airflow obstruction, expect increased FRC and RV (hyperinflation and air trapping) 7
• TLC may be normal or increased in mild-moderate obstruction, but paradoxically not elevated in severe obstruction due to decreased inspiratory capacity 7
• RV/TLC ratio increases with worsening airflow obstruction, indicating air trapping 7

Diffusing Capacity (DLCO) (Strongly Recommended)

• DLCO helps differentiate chronic bronchitis from emphysema - it is typically preserved or only mildly reduced in pure chronic bronchitis but significantly reduced in emphysema 5, 4
• Hemoglobin-adjusted single-breath DLCO should be measured 7
• DLCO decreases progressively with moderate to severe airflow obstruction 7

Clinical Interpretation Framework

Severity Classification Based on FEV1

Once airflow obstruction is confirmed (FEV1/FVC <0.70), classify severity: 5, 2

• Mild: FEV1 60-80% predicted
• Moderate: FEV1 40-59% predicted
• Severe: FEV1 <40% predicted

Pattern Recognition

• Obstructive pattern: Reduced FEV1/FVC ratio with increased FRC and RV, preserved or mildly reduced DLCO suggests chronic bronchitis 8, 7
• Mixed pattern: Reduced FEV1/FVC with reduced TLC and significantly reduced DLCO suggests coexisting emphysema 8
• Normal spirometry effectively excludes COPD 2

Common Pitfalls to Avoid

• Do not rely on clinical diagnosis alone - chronic bronchitis is defined clinically (productive cough ≥3 months/year for 2 consecutive years), but spirometry is mandatory to document airflow obstruction and establish COPD 1, 2, 3
• Do not assume all chronic cough is chronic bronchitis - approximately one-third of patients with chronic cough actually have asthma, which requires spirometry with bronchodilator testing to diagnose 6
• Do not skip DLCO measurement - this is critical for distinguishing chronic bronchitis (preserved DLCO) from emphysema (reduced DLCO), which has important prognostic and therapeutic implications 5
• Do not use FVC alone as a surrogate for TLC - FVC is reduced in both restrictive and obstructive disorders, making it unreliable for distinguishing these patterns 8

Additional Considerations

• In patients with occupational dust exposure (cotton, hemp, linen), the same PFT battery is required to diagnose occupational chronic bronchitis (byssinosis) 1
• Chest radiograph should be obtained to exclude other pathology, though it is not sensitive for chronic bronchitis diagnosis 1
• Consider arterial blood gas if severe obstruction (FEV1 <40%) to assess for hypoxemia and hypercapnia 8