About This Page
This is a clinician-written, evidence-based summary aligned to the 2026 MLA Content Map. It is intended for medical students and junior doctors preparing for the UKMLA. Always cross-reference with NICE guidance, local protocols, and clinical judgement.
The Bottom Line
- Viral upper airway infection causing subglottic oedema — peak age 6 months to 3 years
- Parainfluenza virus (types 1 and 3) is the most common cause
- Classic triad: barking (seal-like) cough + inspiratory stridor + hoarse voice, often worse at night
- First-line: single dose of oral dexamethasone 0.15 mg/kg (or prednisolone if unavailable)
- Severe croup (stridor at rest, significant distress): nebulised adrenaline 1:1000 (5 mL) + oral dexamethasone
Overview
Croup (acute laryngotracheobronchitis) is an acute viral infection of the upper airway causing inflammation and oedema of the subglottic region — the narrowest part of the paediatric airway. The most common causative organism is parainfluenza virus (types 1 and 3), followed by RSV, influenza, adenovirus, and human metapneumovirus. The characteristic barking cough, inspiratory stridor, and hoarse voice result from subglottic narrowing. Symptoms are typically worse at night and often preceded by a coryzal prodrome. Most cases are mild and self-limiting.
Epidemiology
Croup accounts for approximately 5% of emergency paediatric admissions. Peak incidence is between 6 months and 3 years, with boys affected slightly more than girls. It is most common in autumn and early winter. Most children have mild disease that resolves within 48 hours. Approximately 1–8% of children with croup require hospital admission, and less than 1% require intubation.
Clinical Features
Symptoms
Barking cough — characteristic "seal-like" or "brassy" cough, often worse at night
Inspiratory stridor — high-pitched noise on breathing in
Hoarse voice or cry
Low-grade fever and coryzal symptoms (preceding prodrome)
Stridor at rest (moderate-severe croup)
Agitation, exhaustion, cyanosis, or reduced consciousness (severe/life-threatening)
Signs
Inspiratory stridor (biphasic in severe cases)
Sternal and intercostal recession (increased work of breathing)
Tachypnoea
Quiet or absent stridor with reduced air entry = imminent respiratory failure
Investigations
First-line
Clinical diagnosisBased on the characteristic barking cough and stridor — investigations are NOT usually required
Second-line
CXR (if diagnosis uncertain)Steeple sign (subglottic narrowing on AP view) — NOT routinely needed
Pulse oximetrySpO2 <92% indicates severe disease
Specialist
Blood gasOnly in severe/life-threatening cases — rising CO2 indicates respiratory failure
Management
NICE CKS Croup + BTS guidelines1
Mild croup (occasional barking cough, no stridor at rest)
- Can usually be managed at home
- Single dose of oral dexamethasone 0.15 mg/kg
- Supportive: comfort the child (crying worsens symptoms), adequate fluids, monitor
- Safety net: return if stridor at rest, difficulty breathing, or reduced oral intake
2
Moderate croup (frequent barking cough, stridor at rest, some recession)
- Oral dexamethasone 0.15 mg/kg (single dose)
- Observe for at least 2–4 hours after treatment
- If improving, discharge with safety-net advice
3
Severe croup (significant stridor and recession at rest, agitation)
- Nebulised adrenaline 1:1000 (1 mg/mL) — 5 mL nebulised
- Oral dexamethasone 0.15 mg/kg (or IM dexamethasone if unable to take oral)
- Observe for minimum 2 hours after adrenaline (rebound effect possible)
- Supplemental oxygen if SpO2 <92%
- Senior/anaesthetic support if not improving or signs of impending respiratory failure
Complications
- Respiratory failure: Rare but life-threatening — may require intubation
- Bacterial tracheitis: Secondary bacterial infection (Staphylococcus aureus) — presents with high fever, toxicity, and purulent secretions; requires IV antibiotics + intubation
- Recurrent croup: Some children are predisposed — investigate for subglottic stenosis or haemangioma if recurrent
UKMLA Exam Tips
- 1Barking cough + stridor + hoarse voice + age 6 months–3 years + worse at night = croup
- 2Parainfluenza is the most common cause
- 3Oral dexamethasone 0.15 mg/kg is first-line for ALL severities of croup
- 4Nebulised adrenaline for severe croup — observe for at least 2 hours afterwards (rebound)
- 5DO NOT examine the throat of a child with suspected croup or epiglottitis — may precipitate complete airway obstruction
- 6Steeple sign on CXR = subglottic narrowing — but CXR is NOT routinely needed
- 7CROUP vs EPIGLOTTITIS: croup = gradual onset, barking cough, hoarse voice. Epiglottitis = rapid onset, drooling, muffled voice, toxic-looking, NO cough
practicetest your knowledge on croupApply what you've learnt with UKMLA-style questions from the iatroX Q-Bank — respiratory and beyond.
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