A child falls, hits their head, cries, and then seems fine. Every parent and every emergency clinician knows this moment — and the difficult question that follows: does this child need a CT scan, with its radiation, or is careful observation enough?

The PECARN Calculator above applies the Pediatric Emergency Care Applied Research Network prediction rule for head injury. Select the child's age group, check any of the six warning signs that are present, and it reports whether the low-risk criteria are met.

This guide explains what the PECARN rule is, what each predictor means, and how to interpret the result — with the essential reminder that this tool supports clinical judgment and never replaces it.

What Does the PECARN Calculator Do?

The calculator implements the PECARN clinical prediction rule for identifying children at very low risk of clinically important traumatic brain injury after minor head trauma. It covers the two age-specific versions of the rule: under 2 years, and 2 years and older.

You select the age group, which reveals the six predictors for that group, and check every sign that is present. The headline result states whether the low-risk criteria are met or not, with a plain-language explanation of what that means.

The tool is educational. It mirrors the published rule so students, parents, and clinicians can see how the criteria combine — but any real head injury needs professional evaluation.

How to Use the PECARN Calculator

Choose the child's age group from the dropdown: "Under 2 years old" or "2 years or older." The matching set of six checkboxes appears below.

Check every predictor that is present. Be honest and careful — the rule only works when the signs are assessed accurately.

Press Calculate. The verdict and explanation appear in the result panel. Press Reset to start over with a different age group.

What the PECARN Rule Is

The rule was derived by Kuppermann and colleagues and published in The Lancet in 2009, from a study of more than 42,000 children with head injuries seen in emergency departments. It is one of the most validated decision aids in pediatric emergency medicine.

Its purpose is narrow and specific: identify the subgroup of children with minor head trauma whose risk of clinically important brain injury is so low that CT scanning can usually be avoided. It does not diagnose injury — it stratifies risk.

The rule applies to children with GCS scores of 14–15, presenting within 24 hours of injury, with no signs of more severe trauma. Children with obvious severe injuries were never candidates for the rule.

The Under-2 Predictors Explained

For children under 2, the six predictors are: altered mental status (GCS 14, agitation, sleepiness, slow response, or repetitive questioning); occipital, parietal, or temporal scalp hematoma; loss of consciousness of 5 seconds or more; severe mechanism of injury; palpable skull fracture; and not acting normally per the parents.

Each predictor captures a different danger signal. A palpable skull fracture suggests the impact deformed the skull; a non-frontal scalp hematoma in an infant correlates with underlying fracture; parental report of abnormal behavior catches subtle changes clinicians might miss.

The age-specific list exists because infants cannot report headache or vomiting reliably, so the rule leans on observable signs and caregiver report instead.

The Age-2-and-Older Predictors Explained

For children 2 and older, the six predictors are: altered mental status (same definition); any loss of consciousness; vomiting since the injury; severe mechanism of injury; severe headache; and signs of basilar skull fracture.

Older children can report symptoms, so headache and vomiting join the list — both reflect processes inside the skull that infants cannot describe. The loss-of-consciousness threshold also drops from 5 seconds to any duration.

Signs of basilar skull fracture include bruising around the eyes, bruising behind the ears, and fluid leaking from the nose or ears. These are never subtle findings — if present, the child needs emergency care immediately.

What "Low-Risk Criteria Met" Means

When none of the six predictors is present, the child meets the low-risk criteria. In the derivation study, the risk of clinically important traumatic brain injury in this group was extremely low — low enough that routine CT is generally not recommended.

"Very low risk" is not "no risk," and it is not a discharge decision made by a webpage. It is an input to a clinician's judgment, combined with the examination, the family's reliability for observation, and access to follow-up care.

The calculator states this carefully in its result text: the finding supports a clinician's decision-making, and the child still needs medical evaluation.

What "Not Met" Means

When one or more predictors are present, the low-risk criteria are not met. The calculator lists exactly which predictors were checked so the finding is transparent.

This does not mean the child has a brain injury — most children with a predictor still do fine. It means the risk is high enough that CT imaging is usually discussed, and the decision is made with the treating clinician.

Do not wait to seek care when predictors are present. The rule's value is in prompting timely evaluation, not in grading how worried you should be at home.

Worked Example: A Toddler With No Predictors

First: an 18-month-old trips on a rug, cries immediately, and is consolable and playful within minutes. No loss of consciousness, no vomiting, a small frontal bump, acting normally per the parents.

Then: select "Under 2 years old" and check nothing — no predictor is present. Frontal hematomas are notably absent from the predictor list.

Then: the calculator reports low-risk criteria met. In practice, this supports observation at home with clear return precautions, as directed by the child's clinician.

Worked Example: A School-Age Child Who Vomited

First: a 7-year-old falls off playground equipment, briefly loses consciousness, and vomits once in the emergency department waiting room.

Then: select "2 years or older" and check "Any loss of consciousness" and "Vomiting since the injury."

Then: the calculator reports the low-risk criteria are not met, listing both predictors. The clinical team would typically discuss CT imaging — the rule has done its job by flagging the case.

Worked Example: An Infant With a Parietal Hematoma

First: a 10-month-old rolls off a bed and develops a parietal scalp hematoma. The infant is alert, feeding normally, with no loss of consciousness.

Then: select "Under 2 years old" and check "Occipital, parietal, or temporal scalp hematoma" — location matters, and parietal qualifies.

Then: the criteria are not met. A single predictor is enough — the rule requires all six to be absent, and this case shows why location-specific knowledge matters for infants.

Common Mistakes When Applying the Rule

The most dangerous mistake is using the rule on the wrong patient — a child with a GCS below 14, obvious severe trauma, or presentation beyond 24 hours was never in the study population, and the rule's numbers do not apply.

Another error is treating "low risk" as "no risk" and skipping evaluation entirely. The rule informs the CT decision within a clinical encounter; it does not authorize staying home.

People also misjudge the predictors, especially "severe mechanism" — it has a specific definition (high-speed crashes, significant falls, high-impact strikes), not just "it looked scary." When in doubt, describe the mechanism to the clinician rather than classifying it yourself.

CT Scans: Benefit Against Radiation

The entire point of the PECARN rule is to spare low-risk children the radiation of a head CT. A single head CT in childhood carries a small but real increase in lifetime cancer risk, so avoiding unnecessary scans matters at population scale.

But CT remains the right test when the risk warrants it — a missed brain injury is far worse than a justified scan. The rule exists to separate the two groups, not to eliminate scanning.

Shared decision-making is the modern standard: the clinician explains the risk estimate, the family asks questions, and the choice reflects both the evidence and the family's values and observation capacity.

Observation Instructions After a Head Injury

Children who do not get a CT still need careful observation, typically for 24 to 48 hours. Watch for worsening headache, repeated vomiting, unusual sleepiness, confusion, weakness, or unequal pupils.

Wake the child once or twice during the first night's sleep to check they rouse normally — your clinician will specify the schedule. A child who cannot be awakened needs emergency care immediately.

Return precautions should be explicit and written down. The calculator's result is a starting point; the clinician's discharge instructions are the plan you follow.

How to Interpret Your Result Correctly

Read the verdict as a risk stratum, not a diagnosis. "Met" means very low risk in the studied population; "not met" means the risk exceeds the low-risk threshold and imaging is typically discussed.

The listed predictors in a "not met" result are the actionable part — they tell the clinical team exactly which findings drove the classification, which focuses the examination and the conversation.

Never let the calculator overrule a clinician, and never let it substitute for one. If the tool and your instincts disagree about a child's condition, the instincts that say "get help" are the ones to follow.

Where the PECARN Rule Is Used

Emergency departments worldwide use the rule at the bedside, often built into triage protocols and electronic records. It is taught in pediatric emergency medicine as a core decision aid.

Researchers use it as a benchmark for new prediction tools — any challenger must beat PECARN's validated performance. Medical educators use it to teach the difference between risk stratification and diagnosis.

Parents encounter it indirectly whenever a clinician explains why a scan is or is not recommended. Understanding the rule's logic makes those conversations clearer and less frightening.

Frequently Asked Questions

1. What is the PECARN Calculator?

It applies the PECARN pediatric head-injury prediction rule. You select the child's age group, check any of the six warning signs present, and it reports whether the low-risk criteria for important brain injury are met.

2. What does PECARN stand for?

The Pediatric Emergency Care Applied Research Network, a research consortium of pediatric emergency departments. The head-injury rule was derived by Kuppermann and colleagues and published in The Lancet in 2009.

3. What ages does the rule cover?

Children under 18 with minor head trauma, split into two rule versions: under 2 years, and 2 years and older. The predictors differ because infants cannot report symptoms like headache.

4. What are the under-2 predictors?

Altered mental status, occipital/parietal/temporal scalp hematoma, loss of consciousness of 5 seconds or more, severe mechanism of injury, palpable skull fracture, and not acting normally per the parents.

5. What are the predictors for age 2 and older?

Altered mental status, any loss of consciousness, vomiting, severe mechanism of injury, severe headache, and signs of basilar skull fracture.

6. What does "low-risk criteria met" mean?

None of the six predictors is present, placing the child in the very-low-risk group from the derivation study — where routine CT is generally not recommended. It is an input to clinical judgment, not a home discharge decision.

7. Does "not met" mean my child has a brain injury?

No. It means the risk exceeds the low-risk threshold, so CT imaging is usually discussed with the clinician. Most children with a predictor still recover fully.

8. Can I use this instead of going to the emergency department?

No. This tool is educational and never replaces medical evaluation. Any child with a head injury should be assessed by a clinician — call emergency services for a serious injury.

9. Why are the predictor lists different by age?

Infants cannot reliably report headache or vomiting, so their rule uses observable signs and parent report — scalp hematoma location, behavior changes. Older children can describe symptoms, so those join their list.

10. What is a "severe mechanism of injury"?

High-energy events: motor vehicle crashes with ejection or rollover, falls from significant height, being struck by a high-impact object, or similar forces. It has a specific study definition — describe the event to the clinician rather than classifying it yourself.

11. Why does hematoma location matter in infants?

Occipital, parietal, or temporal hematomas in infants correlate with underlying skull fracture, while frontal hematomas — the classic toddler forehead bump — do not carry the same association. That is why only non-frontal locations are predictors.

12. What is clinically important traumatic brain injury?

The study's outcome: death, neurosurgery, intubation for more than 24 hours, or hospital admission of 2+ nights with CT findings. The rule predicts this composite, not every minor concussion symptom.

13. Does the rule apply after 24 hours?

No. The study enrolled children presenting within 24 hours of injury. Beyond that window, the validated risk estimates do not apply — seek care and let the clinician assess directly.

14. What should I watch for at home after a minor head injury?

Worsening headache, repeated vomiting, unusual sleepiness, confusion, weakness, unequal pupils, or inability to be awakened. Any of these needs immediate emergency care.

15. Why avoid CT scans in low-risk children?

Because head CT delivers radiation with a small lifetime cancer risk, and in the very-low-risk group the scan almost never changes management. The rule spares children a test whose benefit does not justify its risk.