Diagnostic Approach to Bronchiolitis
Bronchiolitis is a clinical diagnosis based solely on history and physical examination—routine laboratory tests, chest radiographs, and viral testing should not be ordered. 1, 2
Clinical Diagnostic Criteria
The diagnosis requires identifying a specific constellation of findings in children under 2 years of age 2:
- Viral upper respiratory prodrome (rhinorrhea, congestion) followed by lower respiratory tract involvement 1, 2
- Lower respiratory signs: tachypnea, wheezing, rales/crackles, and cough 2
- Increased respiratory effort: grunting, nasal flaring, intercostal/subcostal retractions 1, 2
Essential History Elements
When evaluating a child with suspected bronchiolitis, specifically assess 2:
- Feeding and hydration status: ability to take oral fluids, signs of dehydration 2
- Mental status changes: lethargy or irritability 2
- Risk factors for severe disease 1, 2:
- Age less than 12 weeks
- History of prematurity
- Hemodynamically significant congenital heart disease
- Chronic lung disease/bronchopulmonary dysplasia
- Immunodeficiency
- In utero smoke exposure
Physical Examination Specifics
Count the respiratory rate for a full 60 seconds to ensure accuracy, as brief observations can be misleading 2. Key findings include 2:
- Tachypnea ≥70 breaths/minute suggests increased risk of severe disease 2
- Work of breathing assessment: nasal flaring, grunting, retractions 3
- Serial observations over time are necessary as the disease state varies 2
What NOT to Order
The American Academy of Pediatrics explicitly recommends against routine diagnostic testing 1, 2:
- No routine chest radiographs: they do not alter management and may lead to inappropriate antibiotic prescribing 2
- No routine viral testing (including RSV testing): does not change clinical management 2
- No routine laboratory studies: blood work is unnecessary in typical cases 1, 2
Common pitfall: Routine diagnostic testing increases costs without improving outcomes and may paradoxically lead to inappropriate antibiotic prescribing when incidental findings are discovered 2.
When Diagnostic Testing May Be Considered
While not routine, testing may be warranted in specific circumstances 4:
- Etiological diagnosis (viral antigen or genome detection) may have a role in reducing hospital transmission of infection 4
- Consider testing only when results would change management decisions or infection control measures
Severity Assessment
After establishing the diagnosis clinically, assess disease severity to guide disposition 1:
- Respiratory rate and work of breathing 3
- Oxygen saturation monitoring (though continuous pulse oximetry should be avoided in stable infants) 3
- Hydration status and feeding ability 3
The diagnosis remains fundamentally clinical, emphasizing that bronchiolitis is a constellation of symptoms and signs rather than a laboratory or radiographic diagnosis 1, 5.