Pecarn Head Injury Calculator
Determine need for CT scan in pediatric minor head trauma using PECARN criteria. Enter values for instant results with step-by-step formulas.
Calculator
Adjust values & calculateHigh-Risk Criteria (CT Recommended if any present)
Intermediate-Risk Criteria (Observation vs CT)
Interpretation
No high-risk or intermediate-risk criteria present. The risk of ciTBI is less than 0.02 percent. CT scan is not recommended, and the child can be safely discharged with appropriate return precautions.
Management Guidance
Discharge with head injury return precautions. Instruct parents on signs requiring emergency evaluation.
Formula
Separate algorithms for children under 2 and 2+ years. High-risk criteria indicate CT recommendation. Intermediate-risk criteria suggest observation vs CT. Absence of all criteria indicates very low risk where CT is not recommended.
Last reviewed: January 2026
Worked Examples
Example 1: 18-Month-Old with Intermediate Risk
Example 2: 5-Year-Old with Low Risk
Background & Theory
The Pecarn Head Injury Calculator applies the following established principles and formulas. Health and medicine calculators are grounded in validated physiological measurement methods established through decades of clinical research. Body Mass Index, or BMI, is calculated by dividing weight in kilograms by height in meters squared (kg/m²), a formula originating from Adolphe Quetelet's 19th-century statistical work and later codified by the WHO into standard classifications: underweight below 18.5, normal weight 18.5 to 24.9, overweight 25 to 29.9, and obese at 30 and above. Basal Metabolic Rate quantifies the minimum energy required to sustain life at rest. The Mifflin-St Jeor equation, published in 1990 and widely regarded as the most accurate for most adults, calculates BMR as (10 × weight in kg) + (6.25 × height in cm) − (5 × age) ± sex adjustment. The older Harris-Benedict equations, revised in 1984 by Roza and Shizgal, remain in common use. Total Daily Energy Expenditure is derived by multiplying BMR by a physical activity factor ranging from 1.2 for sedentary individuals to 1.9 for extremely active ones, following the methodology validated by doubly labeled water studies. Body fat percentage can be estimated without laboratory equipment using the U.S. Navy circumference method, which uses neck, waist, and hip measurements, or via BMI-derived equations adjusted for age and sex. The Jackson-Pollock skinfold method offers higher precision with calipers. Blood pressure classification, according to the American College of Cardiology and the 2017 ACC/AHA guidelines, defines normal as below 120/80 mmHg, elevated as 120 to 129 systolic, and hypertension stage 1 as 130 to 139 systolic or 80 to 89 diastolic. Target heart rate zones for aerobic exercise are derived from maximum heart rate estimates, most commonly using the formula 220 minus age in years, with moderate-intensity training typically defined as 50 to 70 percent of maximum heart rate and vigorous intensity at 70 to 85 percent, consistent with CDC and American Heart Association guidelines. These thresholds guide safe and effective cardiovascular conditioning.
History
The history behind the Pecarn Head Injury Calculator traces back through the following developments. The history of health measurement stretches back to ancient Greece, where Hippocrates around 400 BCE laid the foundation for observational medicine by systematically recording patient symptoms, diet, and environment. His humoral theory, though scientifically superseded, established the principle that the body operates as an interconnected system subject to measurable imbalance. The transformation toward modern medicine accelerated in the 19th century. Louis Pasteur and Robert Koch developed germ theory in the 1860s and 1870s, identifying microorganisms as disease agents and enabling targeted interventions. Florence Nightingale, working during the Crimean War in the 1850s, introduced statistical analysis to nursing practice, demonstrating through data visualization that sanitation reduced mortality. Her work is foundational to evidence-based health measurement. The discovery of vitamins in the early 20th century, beginning with Casimir Funk's coinage of the term in 1912 and culminating in the isolation of vitamins A through K, created the field of nutritional science and gave rise to dietary reference intake frameworks. The World Health Organization, founded in 1948, subsequently established global standards for health metrics, disease classification through the International Classification of Diseases, and recommended daily allowances. The BMI as a clinical screening tool gained traction in the 1970s through Ancel Keys' large-scale epidemiological work, which validated Quetelet's index as a population-level obesity indicator. Through the 1980s and 1990s, the Framingham Heart Study produced landmark data linking cholesterol, blood pressure, and lifestyle factors to cardiovascular disease risk, directly shaping the numeric thresholds still used in health calculators. The evidence-based medicine movement, formalized by Gordon Guyatt and colleagues at McMaster University in the early 1990s, demanded that all health recommendations derive from systematically graded clinical evidence. The digital health era beginning in the 2000s brought these formulas to consumer devices, wearable sensors, and smartphone applications, expanding access to health self-monitoring on a global scale and enabling population-level data collection that continues to refine clinical reference ranges.
Frequently Asked Questions
Sources & References
- 1Kuppermann N, et al. Identification of children at very low risk of clinically-important brain injuries after head trauma. Lancet. 2009;374(9696):1160-1170
- 2Lorton F, et al. Validation of the PECARN clinical decision rule for children with minor head trauma. Acad Emerg Med. 2016;23(12):1429-1435
- 3AAP - Management of Minor Closed Head Injury in Children
Formula
PECARN Algorithm: Age-specific criteria stratify into High Risk, Intermediate Risk, or Low Risk for ciTBI
Separate algorithms for children under 2 and 2+ years. High-risk criteria indicate CT recommendation. Intermediate-risk criteria suggest observation vs CT. Absence of all criteria indicates very low risk where CT is not recommended.
Worked Examples
Example 1: 18-Month-Old with Intermediate Risk
Problem: An 18-month-old fell from a 4-foot high changing table, has a large occipital scalp hematoma, but GCS is 15, no altered mental status, no palpable skull fracture, no loss of consciousness, and parents say the child is acting normally.
Solution: Age group: Under 2 years\nHigh-risk criteria: GCS < 15 (No), Altered mental status (No), Palpable skull fracture (No)\nIntermediate-risk criteria:\n- Scalp hematoma (occipital): YES\n- LOC >= 5 seconds: No\n- Severe mechanism (fall > 3 ft): YES\n- Not acting normally: No\nTwo intermediate criteria present = Intermediate Risk\nciTBI risk: ~0.9%
Result: PECARN: Intermediate Risk (ciTBI ~0.9%) - Observation vs CT based on clinical judgment. Consider CT given two intermediate criteria present.
Example 2: 5-Year-Old with Low Risk
Problem: A 5-year-old fell off a bicycle (no motor vehicle involvement) from standing height, briefly cried, has a small frontal bump, GCS 15, no altered mental status, no signs of basilar skull fracture, no LOC, no vomiting, no headache.
Solution: Age group: 2 years and older\nHigh-risk criteria: GCS < 15 (No), Altered mental status (No), Basilar skull fracture signs (No)\nIntermediate-risk criteria:\n- LOC: No\n- Vomiting: No\n- Severe mechanism: No (fall from standing, no MVC)\n- Severe headache: No\nNo high or intermediate criteria = Low Risk\nciTBI risk: < 0.05%
Result: PECARN: Low Risk (ciTBI < 0.05%) - CT NOT recommended. Discharge with head injury precautions.
Frequently Asked Questions
What is the PECARN pediatric head injury prediction rule?
The PECARN (Pediatric Emergency Care Applied Research Network) head injury prediction rule is an evidence-based clinical decision tool designed to identify children at very low risk of clinically important traumatic brain injury (ciTBI) after minor head trauma. Published by Kuppermann et al. in 2009 in The Lancet, it was developed from a large prospective cohort study of over 42,000 children across 25 emergency departments. The rule uses separate algorithms for children under 2 years and children 2 years and older, stratifying patients into high-risk, intermediate-risk, and low-risk categories. Its primary purpose is to safely reduce unnecessary CT scans while identifying children who need imaging.
Why are there separate PECARN criteria for children under 2 versus 2 and older?
Separate criteria exist because head injury presentation and risk factors differ significantly between these age groups. Children under 2 years are more difficult to assess clinically because they cannot articulate symptoms like headache. Their skulls are thinner and more pliable, making palpable skull fracture a meaningful finding. Non-occipital scalp hematomas are less concerning in older children but significant in infants. Conversely, children 2 and older can report headache and other symptoms. Signs of basilar skull fracture replace palpable skull fracture as a high-risk criterion in the older group. The fall height threshold also differs: greater than 3 feet for children under 2 versus greater than 5 feet for older children.
What is a clinically important traumatic brain injury as defined by PECARN?
PECARN defines clinically important traumatic brain injury (ciTBI) as any of the following outcomes: death from TBI, neurosurgical intervention for TBI (intracranial pressure monitoring, elevation of depressed skull fracture, ventriculostomy, hematoma evacuation, lobectomy, tissue debridement, or dural repair), intubation for more than 24 hours for TBI, or hospital admission for 2 or more nights for TBI with findings on CT. This definition deliberately excludes isolated non-depressed skull fractures and brief hospital admissions for observation alone, as these are not considered clinically important outcomes. The ciTBI definition ensures the rule focuses on injuries that truly require intervention rather than incidental CT findings.
How does the PECARN rule reduce unnecessary CT scans in children?
The PECARN rule reduces unnecessary CT scans by providing a validated method to identify the approximately 95 percent of children with minor head trauma who are at very low risk for ciTBI. Before PECARN, CT utilization rates for pediatric head trauma varied widely between institutions, ranging from 15 to 53 percent. Implementation of the PECARN rule has been shown to reduce CT rates by 20 to 30 percent without missing clinically important injuries. This is particularly important because CT scanning exposes children to ionizing radiation, which carries a small but real increased lifetime cancer risk, estimated at approximately 1 in 5,000 for a head CT in a young child. The negative predictive value of the PECARN rule exceeds 99.9 percent for the low-risk group.
What should clinicians do with intermediate-risk patients on the PECARN algorithm?
Intermediate-risk patients present the most challenging clinical decision point in the PECARN algorithm. These children have approximately 0.8 to 0.9 percent risk of ciTBI, which is low but not negligible. The PECARN rule recommends that the decision to obtain CT versus observe should be based on several factors: physician experience and clinical gestalt, whether symptoms are worsening or improving, the number of intermediate-risk criteria present (more criteria increases concern), patient age (younger children have lower CT threshold), and parental preference. Observation for 4 to 6 hours with serial neurological examinations is a reasonable alternative to immediate CT, with imaging obtained if symptoms worsen or fail to improve.
How reliable is parental assessment that a child is not acting normally after head injury?
Parental or caregiver assessment is a uniquely important criterion in the PECARN rule for children under 2, reflecting the clinical reality that parents often detect subtle behavioral changes that clinicians may miss during a brief emergency department evaluation. Studies validating the PECARN rule found that when parents reported their child was not acting normally, the risk of ciTBI was significantly elevated even when other criteria were absent. This criterion captures a broad range of concerning behaviors including unusual irritability, excessive sleepiness, decreased feeding, and changes in interaction patterns. While subjective, parental concern has been validated as a meaningful predictor and should be taken seriously in clinical decision-making.
References
- Kuppermann N, et al. Identification of children at very low risk of clinically-important brain injuries after head trauma. Lancet. 2009;374(9696):1160-1170
- Lorton F, et al. Validation of the PECARN clinical decision rule for children with minor head trauma. Acad Emerg Med. 2016;23(12):1429-1435
- AAP - Management of Minor Closed Head Injury in Children
Reviewed by Rahul Singh, Health & Wellness Specialist · Editorial policy