How this instrument works
The Pediatric Emergency Care Applied Research Network (PECARN) rule is a clinical decision tool for children evaluated after blunt head trauma who look well enough that a CT scan isn't obviously and immediately necessary — it was derived from 42,412 children across 25 North American emergency departments and published by Kuppermann and colleagues in The Lancet in 2009. Its purpose is to identify which of these children can safely skip a CT scan and which should have one, or be observed, based on findings from the history and physical exam alone.
The rule runs in two steps, and it uses different specific criteria depending on whether the child is under 2 years old or 2 and older, because the signs of a significant head injury present differently at those ages. Step 1 checks for high-risk findings: a Glasgow Coma Scale score under 15 (or other severe altered mental status), a palpable skull fracture (under 2) or signs of a basilar skull fracture (2 and older), or altered mental status of a milder kind — agitation, drowsiness, repetitive questioning, or a slow response to people talking to the child. Any one of these puts a child in the high-risk tier, where the original study found roughly a 4.3-4.4% risk of a clinically important traumatic brain injury (ci-TBI) — an injury serious enough to need neurosurgery, intubation for more than a day, hospital admission for two or more nights, or death caused by the brain injury — and CT imaging is recommended.
If none of the Step 1 findings are present, Step 2 checks a second, age-specific list of intermediate-risk findings — for children under 2: a scalp hematoma anywhere except the forehead, loss of consciousness of 5 seconds or more, a caregiver reporting the child isn't acting normally, or a severe mechanism of injury; for children 2 and older: any history of vomiting, any loss of consciousness at all, a severe headache, or a severe mechanism of injury. Any one of these findings puts a child in the intermediate-risk tier, with roughly 0.8-0.9% ci-TBI risk in the original study. A child with none of the Step 1 or Step 2 findings falls in the low-risk tier, where ci-TBI risk was well under 0.1% (roughly 0.02% under 2, 0.05% and up) — low enough that the study's authors recommend against routine CT for this group.
- Select the child's age band — Under 2 years, or 2 years and older — since the specific criteria differ between the two.
- Answer GCS < 15 (or other severe altered mental status) — Yes if the child's Glasgow Coma Scale is below 15 for any reason.
- Answer the skull fracture question shown for the selected age band: a palpable skull fracture (felt on exam) for under 2, or signs of a basilar skull fracture — bruising around the eyes ("raccoon eyes"), bruising behind an ear (Battle's sign), blood behind the eardrum, or clear fluid leaking from the nose or ears — for 2 and older.
- Answer altered mental status (Step 1) — Yes if the child shows agitation, drowsiness/somnolence, repetitive questioning, or a slow response to verbal communication, even with a normal GCS.
- For children under 2, answer the three under-2 intermediate criteria: a scalp hematoma anywhere except the forehead, loss of consciousness lasting 5 seconds or more, and whether a caregiver reports the child isn't acting normally.
- For children 2 and older, answer the three 2-and-over intermediate criteria: any history of vomiting since the injury, any loss of consciousness at all (any duration), and a severe headache.
- Answer severe mechanism of injury — Yes if any of the following occurred: a fall of more than 3 feet (under 2) or more than 5 feet (2 and older); a high-speed motor vehicle crash involving occupant ejection, a rollover, or a fatality; an unhelmeted pedestrian or cyclist struck by a motor vehicle; or the head struck by a high-impact object.
- Read the risk tier: 0 = low (CT not recommended), 1 = intermediate (discuss observation versus CT with the treating clinician), 2 = high (CT recommended).
Worked example — three children, three tiers
A child under 2 with every field answered No: no Step 1 findings (0 high-risk flags) and no Step 2 findings (0 intermediate-risk flags), so the risk tier is 0, low. In the original PECARN cohort, children under 2 with this profile had under a 0.02% chance of a clinically important brain injury, and the study recommends against routine CT for this group.
The same under-2 child, but now with GCS < 15 answered Yes and everything else still No: that single Step 1 finding is enough on its own — 1 high-risk flag, 0 intermediate-risk flags, risk tier 2, high. CT imaging is recommended regardless of any Step 2 findings, which aren't even relevant once a Step 1 finding is present. This tier carried roughly a 4.4% ci-TBI risk in the original cohort for children under 2.
A child 2 years or older with all Step 1 findings No, but a history of vomiting answered Yes and everything else No: 0 high-risk flags, 1 intermediate-risk flag, risk tier 1, intermediate — about a 0.8% ci-TBI risk in the original study. The rule does not say 'get a CT' at this tier; it calls for a discussion between clinician and caregiver about whether to observe or image, weighing factors like whether the vomiting is isolated or worsening, how experienced the clinician is, and caregiver preference — factors the original study deliberately left to clinical judgment rather than reducing to further hard cutoffs.
Questions
What should I actually do with a 'low', 'intermediate', or 'high' result?
This tool reproduces the PECARN rule's classification, not a treatment decision — always discuss the result with the treating clinician. In the original study, the low-risk tier (no Step 1 or Step 2 findings) carried well under 0.1% risk of a clinically important brain injury and the authors recommend against routine CT; the high-risk tier (any Step 1 finding) carried roughly 4.3-4.4% risk and CT is recommended; the intermediate-risk tier (any Step 2 finding, with no Step 1 finding) carried roughly 0.8-0.9% risk and calls for a shared decision between clinician and caregiver rather than a fixed answer.
What exactly counts as a 'severe mechanism of injury'?
For children under 2: a fall of more than 3 feet, a high-speed motor vehicle crash involving occupant ejection, a rollover, or a fatality, an unhelmeted pedestrian or cyclist struck by a motor vehicle, or the head struck by a high-impact object. For children 2 and older, the list is the same except the fall threshold rises to more than 5 feet. Any one of these qualifies as a severe mechanism in the corresponding age band.
Why doesn't the intermediate tier just tell me whether my child needs a CT?
Because the PECARN study authors deliberately didn't reduce the intermediate-risk group to a further hard yes/no rule. Within that tier, they identified qualitative factors — whether a symptom like vomiting or headache is isolated or occurring alongside others, whether it's worsening on observation, the treating physician's clinical experience, and caregiver preference — that inform the choice between a period of observation and an immediate CT, without those factors being reducible to a simple checklist. This calculator reports the tier; the observation-versus-CT decision within it is meant to be made with a clinician, not by this tool.
What counts as 'altered mental status' if the GCS is already 15?
A child can score a normal GCS of 15 and still show findings the rule treats as a high-risk sign: agitation, drowsiness or somnolence, repetitive questioning, or a slow response to verbal communication. Any of these count as altered mental status for Step 1, independent of the numeric GCS score.
Why are the criteria different for children under 2 versus 2 and older?
Because signs of significant head injury present differently at those ages. Skull fractures in infants and very young children are more reliably felt on exam (palpable skull fracture), while older children can report symptoms like headache and describe loss of consciousness or vomiting more reliably than an infant can. PECARN derived and validated separate criteria for each age band rather than using one set of findings across all ages.
Is this a diagnosis or a substitute for an emergency evaluation?
No. This calculator reproduces a published clinical decision rule for reference; it does not examine the child, and it cannot substitute for in-person evaluation by a clinician. Any child with a concerning head injury — especially with any of the high-risk findings above, or symptoms that are worsening — should be evaluated in person, ideally in an emergency setting, rather than assessed solely through this tool.
What population was the PECARN rule tested on?
Kuppermann et al. derived and validated the rule on 42,412 children under 18 presenting to 25 North American emergency departments within 24 hours of blunt head trauma with a GCS of 14 or 15 (i.e., no more than minor impairment of consciousness), published in The Lancet in 2009. It is one of the largest and most extensively validated pediatric head trauma decision rules in use.
References
- Kuppermann N, et al. — Identification of children at very low risk of clinically-important brain injuries after head trauma: a prospective cohort study. Lancet. 2009;374(9696):1160-70 (PubMed)
- MDCalc — PECARN Pediatric Head Injury/Trauma Algorithm
Read this first: This instrument computes a screening figure from population formulas — it is not a diagnosis, and it cannot see the whole picture a clinician can. Use it to inform a conversation, not to replace one.