Croup is diagnosed primarily by its symptoms, not by lab tests or imaging. A doctor can usually identify it based on three hallmark signs: a harsh, barking cough, a high-pitched whistling sound when your child breathes in (called stridor), and a hoarse voice. Most children with croup never need a blood test, throat swab, or X-ray.
If your child has developed a cough that sounds startlingly like a seal barking, especially in the middle of the night, you’re likely dealing with croup. Here’s how doctors confirm it and what they look for to rule out more serious conditions.
What Croup Sounds and Looks Like
The barking cough is the single most recognizable feature. When swelling narrows the airway around the vocal cords, air forced through that tight space produces a sound distinctly different from a normal cough. Parents often describe it as a seal bark or a dog-like yelp. It’s the kind of cough that, once you hear it, you won’t confuse with anything else.
Alongside the cough, you may notice your child’s voice sounds raspy or hoarse. Breathing in can produce stridor, a high-pitched squeaky or whistling noise. These symptoms almost always get worse at night, and crying or agitation makes them worse still, which can create a frustrating cycle: the cough scares the child, the distress tightens the airway further, and the cough intensifies.
Croup most commonly affects children between 6 and 36 months old. It typically starts like a regular cold, with a runny nose and mild fever for a day or two, before the barking cough appears suddenly, often after the child has gone to bed.
How Doctors Make the Diagnosis
A pediatrician or emergency room doctor diagnoses croup by listening to the cough, observing your child’s breathing, and asking about how quickly symptoms developed. There is no specific test for croup. Routine viral testing, such as PCR swabs, is not recommended for children who present with typical croup symptoms, according to clinical guidelines from Johns Hopkins All Children’s Hospital.
The physical exam focuses on a few key things: whether stridor is present only when the child is upset or also when resting quietly, how hard the chest muscles are working to pull in air (visible as the skin tugging inward between the ribs or at the base of the throat), and whether the child’s skin color looks normal. A child who is alert, has stridor only when crying, and shows no skin color changes has mild croup. A child with stridor at rest, visible chest retractions, or bluish discoloration around the lips is in a more serious category.
How Severity Gets Assessed
Doctors use a standardized scoring system called the Westley Croup Score to gauge how severe an episode is. It evaluates five things, each assigned a point value:
- Stridor: None (0 points), present only with agitation (1), or present at rest (2).
- Chest retractions: None (0), mild (1), moderate (2), or severe (3).
- Air entry: Normal breath sounds (0), decreased (1), or markedly decreased (2).
- Skin color (cyanosis): Normal (0), bluish tint with agitation (4), or bluish tint at rest (5).
- Level of consciousness: Normal or sleeping (0), or disoriented (5).
A total score of 2 or less indicates mild croup, which accounts for the majority of cases. Scores of 3 to 7 suggest moderate croup, and anything above 7 is severe. Most parents will never need to calculate this themselves, but understanding the criteria helps you know what doctors are watching for: stridor at rest, labored breathing, and any change in alertness or skin color are the red flags that bump severity up quickly.
When Imaging Is Used
X-rays are not needed for a straightforward croup diagnosis but are sometimes ordered when the doctor wants to rule out something else, like a foreign object stuck in the airway or a more dangerous condition called epiglottitis. On a neck X-ray, croup produces a characteristic narrowing of the airway below the vocal cords, sometimes called the “steeple sign” because the tapered shape resembles a church steeple. Epiglottitis, by contrast, shows an enlarged flap of tissue at the top of the airway, known as the “thumb sign.”
Ruling Out More Serious Conditions
The biggest diagnostic priority is making sure the barking cough and stridor aren’t caused by something more dangerous. Two conditions in particular can mimic croup.
Epiglottitis
Epiglottitis is a bacterial infection of the tissue that covers the windpipe during swallowing. It comes on suddenly and progresses fast. A child with epiglottitis typically has a high fever, drools because swallowing is too painful, and sits leaning forward with their neck extended to keep the airway open. The barking cough that defines croup is usually absent in epiglottitis. Epiglottitis is most common in children aged 2 to 8, especially those not vaccinated against Haemophilus influenzae type B, while croup peaks at a younger age. If a doctor suspects epiglottitis, they will act quickly because the airway can close rapidly.
Bacterial Tracheitis
Bacterial tracheitis can start out looking exactly like croup but then takes a turn. The key difference is that it doesn’t respond to standard croup treatment. A child with viral croup who receives a dose of nebulized epinephrine in the emergency room typically improves noticeably. A child with bacterial tracheitis shows little or no improvement. These children also tend to look sicker overall, with higher fevers than the low-grade temperatures seen in typical croup. If your child has been treated for croup but keeps getting worse or doesn’t improve with medication, bacterial tracheitis is one of the things doctors will consider.
What You Can Identify at Home
Parents can recognize croup with reasonable confidence before ever reaching a doctor’s office. The combination of a cold that turns into a seal-bark cough, a hoarse voice, and noisy breathing, particularly if your child is between 6 months and 3 years old and it’s fall or early winter, points strongly toward croup.
What you’re watching for at home is whether symptoms stay mild or escalate. Mild croup means the barking cough comes in bouts but your child breathes comfortably between them, eats and drinks normally, and remains alert and playful. Signs that the episode is becoming more serious include stridor that continues even when your child is calm and resting, visible pulling of the skin around the ribs or neck with each breath, difficulty drinking fluids, and unusual drowsiness or agitation that doesn’t settle. Any bluish color around the lips or fingertips warrants an immediate trip to the emergency room.
Cool night air or steam from a hot shower are traditional home remedies parents try while deciding whether to seek care. Neither has strong evidence behind it, but many parents report that stepping outside into cool air for a few minutes seems to ease the cough temporarily. If that provides relief and your child settles back to sleep breathing comfortably, you’re likely dealing with a mild episode that can wait for a doctor’s visit in the morning.