Diagnosing Croup
Croup is a clinical diagnosis based on the characteristic presentation of barking cough, inspiratory stridor, and respiratory distress in children aged 6 months to 6 years, without requiring laboratory tests or imaging in typical cases. 1, 2, 3
Clinical Presentation
The diagnosis relies on recognizing the classic triad:
- Barking or "seal-like" cough that distinguishes croup from other respiratory illnesses 2, 3
- Inspiratory stridor, which may be present only with agitation in mild cases or at rest in moderate-to-severe disease 1, 4
- Respiratory distress with varying degrees of intercostal retractions and increased work of breathing 4, 3
- Preceding upper respiratory symptoms including low-grade fever and coryza, though fever is not required for diagnosis 2, 3
The typical patient is between 6 months and 3 years of age, with symptoms often occurring in late fall or early winter. 2, 5
Severity Assessment
Mild croup: Stridor only with agitation, minimal or no intercostal retractions, normal air entry 1, 4
Moderate-to-severe croup: Stridor at rest, intercostal retractions, increased work of breathing, decreased air entry 1, 4
When Diagnostic Testing is NOT Needed
- Radiographic studies should be avoided in typical presentations as they are unnecessary and delay treatment 1, 3
- Laboratory studies including viral cultures and rapid antigen testing have minimal impact on management and are not routinely recommended 3
- Lateral neck radiographs should not be relied upon as clinical assessment is more accurate 1
Critical Differential Diagnoses to Exclude
Before confirming croup, consider these life-threatening alternatives:
- Bacterial tracheitis: High fever, toxic appearance, purulent secretions 1, 2
- Epiglottitis: Drooling, tripod positioning, muffled voice, high fever (now rare due to Hib vaccination) 2, 5
- Foreign body aspiration: Sudden onset without prodrome, unilateral findings, history of choking episode 1, 2
- Retropharyngeal or peritonsillar abscess: Severe dysphagia, neck stiffness, asymmetric findings 2, 5
- Pertussis: Cough lasting ≥2 weeks with paroxysms, post-tussive vomiting, inspiratory whooping 6
When to Consider Alternative Diagnoses
Obtain imaging (chest X-ray or lateral neck film) or laryngoscopy only when:
- Atypical presentation without the classic barking cough 3
- Sudden onset suggesting foreign body aspiration 1
- Toxic appearance suggesting bacterial tracheitis or epiglottitis 2
- Unilateral findings on examination 2
- Failure to respond to standard croup treatment 3
Common Diagnostic Pitfalls
- Performing unnecessary radiographs in typical cases delays treatment and provides no benefit 1, 3
- Confusing agitation for worsening disease when the child may simply be hypoxic and require oxygen 1
- Missing foreign body aspiration by not asking about sudden onset and choking history 1, 2
- Blind finger sweeps should never be performed in suspected foreign body cases as this may push objects deeper into the airway 1
Etiology
Parainfluenza viruses (types 1-3) cause the majority of croup cases, with types 1 and 2 being most common. 6 Other viral causes include respiratory syncytial virus, influenza, adenovirus, and human metapneumovirus. 6