What labs should be ordered for a patient with suspected Chronic Obstructive Pulmonary Disease (COPD)?

Laboratory Tests for Suspected COPD

Spirometry is the essential laboratory test required for diagnosing COPD, as it provides objective measurement of airflow limitation that cannot be determined by symptoms or physical examination alone. 1

Primary Diagnostic Testing

Spirometry (Required)

• Post-bronchodilator spirometry showing FEV1/FVC ratio <0.70 is the diagnostic criterion for COPD 1
• Spirometry should measure:
  • FEV1 (Forced Expiratory Volume in 1 second)
  • FVC (Forced Vital Capacity)
  • FEV1/FVC ratio
• A post-bronchodilator fixed ratio of FEV1/FVC less than 0.70 confirms airflow limitation 1
• Normal spirometry effectively excludes COPD diagnosis 1

Bronchodilator Reversibility Testing

• Perform to distinguish COPD from asthma 1
• Positive response defined as:
  • Increase in FEV1 by 200 ml AND 15% of baseline value 1
• Substantial bronchodilator response suggests possible asthma, though many COPD patients show some degree of response 1

Secondary Testing

Chest Radiography

• Not needed for diagnosis of mild COPD 1
• Indicated for moderate to severe disease to:
  • Exclude alternative diagnoses
  • Identify emphysematous bullae
  • Rule out serious underlying conditions like lung cancer 1

Arterial Blood Gas Analysis

• Indicated for patients with severe COPD (FEV1 <40% predicted) 1
• Essential to identify:
  • Persistent hypoxemia
  • Hypercapnia
  • Acid-base status 1
• Cannot be reliably predicted by spirometry values 2

Corticosteroid Reversibility Testing

• Recommended for moderate to severe disease 1
• Protocol:
  • Oral prednisolone 30 mg daily for two weeks OR
  • Inhaled corticosteroid (e.g., beclomethasone 500 μg twice daily) for six weeks
• Positive response: same criteria as bronchodilator testing (200 ml AND 15% improvement in FEV1) 1
• Identifies patients who may benefit from inhaled corticosteroids 1

Additional Testing Based on Clinical Context

Complete Blood Count

• To identify:
  • Anemia (which may worsen symptoms)
  • Polycythemia (hematocrit >47% in women or >52% in men) 1

COPD Assessment Test (CAT)

• Validated questionnaire to assess health status impairment 3
• Correlates with:
  • Disease severity
  • Number of exacerbations
  • Healthcare utilization
  • Response to treatment 3

Important Considerations

Diagnostic Pitfalls

• Relying solely on history and physical examination is neither sensitive nor specific for diagnosing COPD 4
• Only about one-third of patients with a diagnosis of COPD have had confirmatory spirometry 4
• Spirometry criteria that apply to asthma cannot be safely applied to COPD patients 2
• Spirometry alone cannot predict hypoxemia in COPD; arterial blood gas analysis is necessary 2

Testing Algorithm

1. Perform spirometry in all patients with respiratory symptoms and risk factors
2. If post-bronchodilator FEV1/FVC <0.70, diagnose COPD
3. Assess severity based on FEV1 percent predicted:
   • Mild: 60-80%
   • Moderate: 40-59%
   • Severe: <40% 1
4. For moderate to severe disease, add:
   • Chest radiography
   • Corticosteroid reversibility testing
   • Arterial blood gas analysis (if severe)
   • Complete blood count

By following this evidence-based approach to laboratory testing, clinicians can accurately diagnose COPD, assess its severity, and guide appropriate treatment decisions to reduce morbidity and mortality.