What are the steps to confirm a diagnosis of croup?

How to Confirm a Diagnosis of Croup

Croup is diagnosed clinically based on the sudden onset of a distinctive barking cough accompanied by stridor, hoarse voice, and respiratory distress—radiographic studies and laboratory tests are unnecessary and should be avoided unless you suspect an alternative diagnosis. 1, 2, 3

Clinical Diagnostic Criteria

The diagnosis of croup is confirmed by identifying these key clinical features:

• Sudden onset of distinctive "barking seal" cough that is the hallmark of the condition 4, 5, 6
• Inspiratory stridor (harsh, high-pitched breathing sound) that may progress to biphasic stridor in more severe cases 3, 5
• Hoarse voice or cry resulting from laryngeal inflammation 4, 3
• Respiratory distress manifested by accessory muscle use, tracheal tug, sternal/subcostal/intercostal retractions 1, 7
• Typically occurs without fever or antecedent respiratory symptoms like prolonged cough or congestion, distinguishing it from other respiratory illnesses 1

The median age of presentation is 23 months, with 63% being male patients 8

Immediate Assessment Focus

When evaluating a child with suspected croup, assess these specific severity indicators immediately:

• Ability to speak or cry normally (loss indicates more severe obstruction) 1
• Presence of stridor at rest versus only with agitation (stridor at rest indicates moderate-to-severe disease) 1, 2
• Respiratory rate and heart rate (tachypnea >70 breaths/min is a hospitalization criterion) 1, 2
• Use of accessory muscles and degree of chest wall retractions 1, 7
• Oxygen saturation (hypoxemia <92-94% indicates severe disease) 1, 2
• Level of agitation or distress (agitation may indicate hypoxia rather than anxiety) 1, 7

Life-threatening signs requiring immediate intervention include silent chest, cyanosis, fatigue/exhaustion, or poor respiratory effort. 1

What NOT to Do

Do not obtain radiographic studies for typical croup presentations—lateral neck radiographs and chest X-rays are unnecessary, do not change management, and should be reserved only for cases where you suspect alternative diagnoses like foreign body aspiration, bacterial tracheitis, or retropharyngeal abscess. 1, 2, 3

Do not perform laboratory studies including viral cultures or rapid antigen testing, as these have minimal impact on management and are not routinely recommended. 3

Do not perform laryngoscopy for straightforward croup diagnosis—reserve this for patients who fail to respond to standard treatment (3+ doses of racemic epinephrine) or when alternative diagnoses are suspected. 7, 3

Critical Differential Diagnoses to Exclude

While croup is diagnosed clinically, you must actively consider and exclude these alternative diagnoses that can mimic croup:

• Bacterial tracheitis: Suspect when the patient fails to respond to standard croup treatment or appears toxic 1, 7
• Foreign body aspiration: Consider if there is sudden onset without prodrome, unilateral findings, or witnessed choking episode 1, 7
• Epiglottitis: Now rare due to Hib vaccination, but presents with drooling, tripod positioning, and toxic appearance 3, 9
• Retropharyngeal or peritonsillar abscess: Consider if there is severe dysphagia, neck stiffness, or asymmetric findings 1, 9

When to Pursue Further Investigation

If a patient fails to respond to standard treatment (corticosteroids and up to 3 doses of nebulized epinephrine), proceed directly to laryngoscopy and bronchoscopy to visualize the airway and identify alternative pathology such as bacterial tracheitis or foreign body. 7

The American Academy of Pediatrics explicitly recommends further workup when standard treatment fails to avoid missing croup-mimicking conditions. 7

Common Diagnostic Pitfalls

• Ordering unnecessary imaging in typical presentations, which delays treatment and exposes children to radiation without benefit 1, 2
• Failing to recognize that an agitated child may be hypoxic rather than simply anxious—agitation is an indication for oxygen therapy 1
• Missing alternative diagnoses by not considering bacterial tracheitis in patients who fail standard treatment 7
• Relying on fever presence or absence—while low-grade fever may occur, it is not necessary for diagnosis 3, 9