How to Diagnose Bronchitis
Bronchitis is a clinical diagnosis based on history and physical examination alone, without routine diagnostic testing. 1
Acute Bronchitis Diagnosis
Clinical Criteria
The diagnosis requires:
- Acute cough (with or without sputum production) as the primary symptom 2
- Duration typically 2-3 weeks 2, 3
- Absence of pneumonia on clinical assessment 1
Key Diagnostic Approach
No routine investigations are recommended for immunocompetent adult outpatients with suspected acute bronchitis. 1 This means:
- No chest x-ray
- No spirometry or peak flow measurement
- No sputum cultures
- No viral PCR testing
- No C-reactive protein or procalcitonin levels
Critical Differential Diagnoses to Exclude
You must clinically rule out conditions that require different management:
Pneumonia - suspect if patient has:
- Tachypnea
- Tachycardia
- Dyspnea
- Lung findings suggestive of consolidation 3
- Only then obtain chest radiography
Pertussis - suspect if:
- Cough persisting >2 weeks
- Paroxysmal cough, whooping, or post-tussive emesis
- Recent pertussis exposure 3
Asthma exacerbation or cough-variant asthma - particularly important as retrospective studies show 65% of patients with recurrent "acute bronchitis" episodes actually have mild asthma 1
COPD exacerbation - in patients with smoking history or known chronic lung disease 1
COVID-19 or influenza - consider testing if clinically indicated based on symptoms and epidemiology 2
When to Investigate
Targeted investigations should only be considered if:
- The acute bronchitis persists or worsens 1
- Patient returns for reassessment
At that point, consider:
- Chest x-ray
- Sputum culture
- Peak expiratory flow rate
- Complete blood count
- Inflammatory markers (CRP) 1
Chronic Bronchitis Diagnosis
For chronic bronchitis, the diagnosis is based on symptoms alone - specifically chronic productive cough. 4 However, the evidence base emphasizes that other respiratory and cardiac causes for chronic productive cough must be excluded through appropriate clinical evaluation. 4
Common Pitfalls to Avoid
Do not order routine chest x-rays - this leads to unnecessary radiation exposure and healthcare costs without improving outcomes 1
Do not rely on sputum color - green or purulent sputum does not reliably differentiate bacterial from viral infection and should not trigger antibiotic use 5
Do not misdiagnose recurrent episodes - if a patient has had multiple episodes of "acute bronchitis," strongly consider underlying asthma as the actual diagnosis 1
Avoid the term "bronchitis" with patients - instead call it a "chest cold" to reduce expectations for antibiotics and testing 2, 3