A health professional usually diagnoses croup from a physical examination and a medical history. During the physical examination, the health professional listens to your child's chest and back and looks for signs of inflammation or infection in the nose, ears, mouth, and throat. You will also be asked when your child's symptoms began, whether they have changed, and whether you have noticed any fever.

Special exams or tests usually are not needed to diagnose croup. However, because the condition may cause difficulty breathing, a pulse oximeter may be placed on your child's finger, toe, or earlobe to check the amount of oxygen in the blood. Rarely, an X-ray may be needed to look at the throat.