Which sign is most characteristic of croup?

• A. Hematemesis
• B. Petechiae
• C. Stridor
• D. Diarrhea

Answer: (C)

Swelling of the larynx and subglottic area from croup narrows the upper airway, and that narrowing produces inspiratory stridor — a high-pitched, harsh sound heard when you breathe in. Stridor is the hallmark sign because it directly reflects the airway obstruction at the level of the throat in croup, often worse at night or with agitation as swelling increases. The other signs listed don’t fit with croup: hematemesis is vomiting blood, which points to GI or bleeding issues; petechiae are tiny hemorrhages that suggest a bleeding or infectious process elsewhere; diarrhea is gastrointestinal and not a defining feature of upper airway inflammation. So the presence of stridor best indicates croup.