PERC Calculator
Use our free Perccalculator Calculator to get personalized health results. Based on validated medical formulas and clinical guidelines.
Calculator
Adjust values & calculatePERC rule satisfied. In a low pretest probability patient, PE is effectively ruled out. No further workup (D-dimer or CT angiography) is needed.
Formula
The PERC rule evaluates 8 binary criteria. If ALL 8 are absent in a patient with low pretest probability (< 15% or Wells score <= 4), PE probability is < 2% and no further testing is needed. If ANY criterion is present, the PERC rule is not satisfied and further workup is indicated.
Last reviewed: January 2026
Worked Examples
Example 1: PERC-Negative Low-Risk Patient
Example 2: PERC-Positive Patient Requiring Workup
Background & Theory
The PERC 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 PERC 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
Formula
PERC Rule: All 8 criteria must be NEGATIVE to rule out PE
The PERC rule evaluates 8 binary criteria. If ALL 8 are absent in a patient with low pretest probability (< 15% or Wells score <= 4), PE probability is < 2% and no further testing is needed. If ANY criterion is present, the PERC rule is not satisfied and further workup is indicated.
Worked Examples
Example 1: PERC-Negative Low-Risk Patient
Problem: A 38-year-old woman presents with mild chest discomfort. No prior VTE, no surgery, no estrogen use, no hemoptysis, no leg swelling, HR 82, SpO2 98%. Wells score is 1 (low risk). Apply the PERC rule.
Solution: PERC Criteria Assessment:\nAge >= 50: No (age 38)\nHR >= 100: No (HR 82)\nSpO2 < 95%: No (SpO2 98%)\nPrior DVT/PE: No\nRecent surgery/trauma: No\nHemoptysis: No\nEstrogen use: No\nUnilateral leg swelling: No\n\nAll 8 criteria are NEGATIVE.
Result: PERC: Negative (0/8 criteria met) | PE effectively ruled out | No D-dimer or CTPA needed
Example 2: PERC-Positive Patient Requiring Workup
Problem: A 55-year-old man on no medications presents with acute dyspnea. HR 105, SpO2 93%, no prior VTE, no recent surgery. Wells score is 3 (low risk). Apply PERC.
Solution: PERC Criteria Assessment:\nAge >= 50: YES (age 55)\nHR >= 100: YES (HR 105)\nSpO2 < 95%: YES (SpO2 93%)\nPrior DVT/PE: No\nRecent surgery/trauma: No\nHemoptysis: No\nEstrogen use: No\nUnilateral leg swelling: No\n\n3 of 8 criteria are POSITIVE.
Result: PERC: Positive (3/8 criteria met) | Cannot rule out PE | Proceed to D-dimer testing
Frequently Asked Questions
What is the PERC rule and when should it be applied?
The PERC (Pulmonary Embolism Rule-out Criteria) rule is a clinical decision tool designed to identify emergency department patients with such low risk of pulmonary embolism that no further diagnostic testing is needed. It was developed by Kline and colleagues in 2004 and validated in subsequent multicenter studies. The rule consists of 8 clinical criteria that can be assessed at the bedside without any laboratory testing. Crucially, the PERC rule should ONLY be applied to patients already determined to have a low pretest probability of PE (typically less than 15%) using gestalt clinical assessment or a validated scoring system like the Wells criteria. If all 8 PERC criteria are negative in a low-risk patient, the probability of PE is less than 2%, which falls below the test threshold and no further workup is indicated.
What are the eight PERC criteria and why were they selected?
The eight PERC criteria are: age 50 years or older, heart rate 100 bpm or greater, oxygen saturation below 95% on room air, prior history of DVT or PE, recent surgery or trauma within the past 4 weeks, hemoptysis, exogenous estrogen use (oral contraceptives, hormone replacement therapy), and unilateral leg swelling. These criteria were selected through logistic regression analysis of a large derivation cohort of emergency department patients evaluated for possible PE. Each criterion independently contributes to PE risk, and their combination provides high sensitivity for identifying patients who may have PE. The criteria encompass physiological signs of PE (tachycardia, hypoxemia), known risk factors (prior VTE, surgery, estrogen use), demographic factors (age), and clinical findings suggestive of DVT (leg swelling) or PE (hemoptysis).
How sensitive and specific is the PERC rule for pulmonary embolism?
The PERC rule has a sensitivity of approximately 97-98% and a negative predictive value exceeding 99% when applied to low-pretest-probability patients. This means that fewer than 2% of patients who satisfy all PERC criteria (all negative) will actually have a PE. The specificity is relatively low at approximately 20-22%, meaning many patients who fail the PERC rule will not have PE but will require further testing. The high sensitivity is the critical performance metric because the primary goal of the PERC rule is to safely rule out PE without missing cases. The landmark PROPER trial (2018) demonstrated that a PERC-based strategy was noninferior to conventional D-dimer-based workup, with a 3-month PE rate of 0.1% in PERC-negative patients. This performance makes the PERC rule one of the most reliable clinical decision tools in emergency medicine.
What is the relationship between the PERC rule and D-dimer testing?
The PERC rule and D-dimer testing serve complementary roles in the PE diagnostic pathway but operate at different steps. The PERC rule is applied first, before any laboratory testing, and if all criteria are negative in a low-risk patient, D-dimer is NOT needed. This is important because D-dimer testing, while highly sensitive, has poor specificity and leads to many false-positive results that trigger unnecessary CT pulmonary angiography (CTPA). Studies show that up to 30-40% of D-dimer tests ordered in the ED are abnormal, but only 5-10% of subsequent CTPAs are positive for PE. By applying the PERC rule first, clinicians can avoid this cascade of testing in truly low-risk patients. If the PERC rule is not satisfied, then D-dimer testing becomes the next appropriate step, followed by CTPA if the D-dimer is elevated.
What happens if a patient fails the PERC rule?
Failing the PERC rule (having one or more positive criteria) does not mean the patient has PE; it simply means that PE cannot be safely ruled out by clinical criteria alone and further diagnostic evaluation is warranted. The next step depends on the overall clinical pretest probability. For patients with low to moderate pretest probability who fail PERC, a D-dimer test should be ordered. If the D-dimer is negative (below the age-adjusted or standard cutoff), PE is effectively ruled out. If the D-dimer is positive, CT pulmonary angiography is the next step. For patients with high pretest probability, the PERC rule should not have been applied in the first place, and CTPA should be obtained directly. It is essential to understand that the PERC rule is a rule-out tool only and cannot be used to rule in PE or estimate the probability of PE in positive cases.
Can the PERC rule be used in hospitalized or critically ill patients?
The PERC rule was specifically developed and validated for use in the emergency department setting in ambulatory patients presenting with symptoms potentially suggestive of PE. It has not been validated for use in hospitalized patients, critically ill ICU patients, or postoperative patients, and should not be applied in these settings. Hospitalized patients often have different baseline characteristics including higher rates of immobility, recent procedures, and comorbidities that fundamentally alter the pretest probability of PE. Additionally, the PERC rule criteria such as oxygen saturation and heart rate may be abnormal for reasons unrelated to PE in critically ill patients. For inpatients suspected of having PE, direct diagnostic imaging with CTPA or ventilation-perfusion scanning is generally recommended, guided by clinical assessment and possibly D-dimer testing depending on the clinical context.
References
Reviewed by Rahul Singh, Health & Wellness Specialist · Editorial policy