How to Diagnose Bronchiolitis
Bronchiolitis is diagnosed clinically based on history and physical examination alone—do not routinely order chest radiographs, viral testing, or laboratory studies. 1, 2
Clinical Diagnostic Criteria
The diagnosis requires identifying a characteristic pattern in children younger than 2 years of age:
- Viral upper respiratory prodrome (rhinorrhea, congestion) followed by progression to lower respiratory tract symptoms 1, 2
- Lower respiratory signs including cough, tachypnea, wheezing or crackles on auscultation 1
- Increased work of breathing manifested as grunting, nasal flaring, intercostal and/or subcostal retractions 1
The physical examination should focus on respiratory rate (count over a full minute), presence of retractions, and auscultatory findings rather than relying on ancillary testing 1, 2.
Critical Risk Stratification
Immediately assess for high-risk factors that predict severe disease: 1, 2
- Age less than 12 weeks
- History of prematurity (less than 37 weeks gestation)
- Hemodynamically significant congenital heart disease
- Chronic lung disease (bronchopulmonary dysplasia)
- Immunodeficiency or immunocompromised state
These infants require closer monitoring and have different management thresholds, as they are at increased risk for progression to severe disease, ICU admission, or mechanical ventilation 1.
Severity Assessment Parameters
Evaluate the following to determine disease severity and need for hospitalization: 1, 2
- Respiratory rate: Tachypnea ≥70 breaths/minute indicates increased severity risk 1, 2
- Oxygen saturation: Check if SpO₂ persistently falls below 90% 2
- Feeding ability: Assess for decreased intake or difficulty feeding 2
- Hydration status: Look for signs of dehydration 1
- Mental status changes or presence of apnea 1
Young infants with bronchiolitis may develop apnea, which has been associated with increased risk for prolonged hospitalization and intensive care 1.
What NOT to Do
Avoid routine diagnostic testing—it does not improve outcomes and leads to unnecessary interventions: 1, 2
- No routine chest radiographs: Approximately 25% of hospitalized infants have atelectasis or infiltrates commonly misinterpreted as bacterial pneumonia, leading to unnecessary antibiotic use 2
- No routine viral testing unless needed for infection control purposes 1, 2
- No routine laboratory studies unless specific concerns for bacterial coinfection exist 1, 2
The absence of tachypnea correlates with lack of lower respiratory tract infection, making clinical assessment more valuable than imaging 1.
Important Differential Considerations
While bronchiolitis is a clinical diagnosis, remain alert to: 2
- Bacterial pneumonia with consolidation (though routine chest X-rays are not recommended to exclude this)
- Acute otitis media (occurs in 50-62% of cases and should be managed per standard otitis media guidelines when identified)
- Serious bacterial infection in febrile infants less than 28 days old (approximately 10% risk—these infants require evaluation per standard fever protocols)
Common Pitfalls to Avoid
- Do not diagnose based on age cutoffs alone—the clinical presentation (viral prodrome followed by lower respiratory symptoms) is what defines bronchiolitis 1
- Do not order tests to "rule out" other diagnoses in typical presentations—this increases costs and leads to overtreatment 1, 2
- Do not assume fever indicates bacterial infection—fever alone does not justify antibiotics, as serious bacterial infection risk is less than 1% in older infants with bronchiolitis 2
- Serial clinical observations may be needed as the physical examination reflects variability in disease state over time 1