Initial Diagnostic Approach for Suspected Acute Bronchitis
For immunocompetent adult outpatients with suspected acute bronchitis, no routine diagnostic tests are recommended—the diagnosis is clinical, based on history and physical examination alone. 1
Clinical Diagnosis
The diagnosis of acute bronchitis requires:
- Acute cough (typically lasting 1-3 weeks) due to inflammation of the trachea and large airways 1, 2, 3
- Absence of pneumonia on clinical assessment 1, 2
- No alternative explanation such as asthma exacerbation, COPD exacerbation, or heart failure 1, 3
What Tests NOT to Order Routinely
The CHEST Expert Panel explicitly recommends against routine use of: 1
- Chest x-ray
- Spirometry or peak flow measurement
- Sputum culture
- Viral PCR testing (including respiratory syncytial virus)
- C-reactive protein (CRP)
- Procalcitonin
- Complete blood count 4
Critical rationale: A systematic review found zero eligible studies demonstrating that any of these tests add predictive value over clinical assessment alone for ruling out pneumonia, influenza, pertussis, asthma, or COPD exacerbation. 1
When to Suspect Pneumonia Instead
Order a chest x-ray only if clinical features suggest pneumonia: 1, 5, 2
- Tachypnea (respiratory rate ≥24-30 breaths/min)
- Tachycardia (heart rate ≥100 beats/min)
- Fever (temperature ≥37.8°C)
- Focal consolidation, egophony, or increased fremitus on chest examination
- Dyspnea at rest
- Oxygen saturation <95-98%
Common pitfall: Do not assume purulent or colored sputum indicates bacterial infection requiring antibiotics or testing—sputum color does not reliably differentiate viral from bacterial etiology. 5, 6
When to Consider Testing for Specific Pathogens
Test for pertussis (PCR or culture) if: 2, 3
- Cough persisting >2 weeks with paroxysmal character
- Post-tussive vomiting
- Inspiratory whooping sound
- Recent pertussis exposure
Test for influenza or COVID-19 if: 3
- Presentation during peak season
- Positive epidemiologic exposure
- Testing would change management (antiviral therapy consideration)
Reassessment Strategy
If cough persists or worsens beyond the expected 2-3 week course, advise the patient to return for reassessment and consider targeted investigations: 1
- Chest x-ray (to exclude pneumonia, malignancy, or structural abnormalities)
- Peak expiratory flow rate or spirometry (to evaluate for asthma—65% of patients with recurrent "acute bronchitis" actually have mild asthma) 1, 7
- Sputum culture (if bacterial superinfection suspected)
- Complete blood count and inflammatory markers like CRP (if complicating infection suspected)
Critical pitfall: Recurrent episodes of "acute bronchitis" should prompt evaluation for underlying asthma, which is commonly misdiagnosed as repeated infections. 1, 7