PERC Calculator - Pulmonary Embolism Rule-Out Criteria
Calculate PERC score, rule-out classification, and positive criteria count based on eight clinical assessment inputs. PERC Calculator - Pulmonary Embolism Rule-Out Criteria helps clinicians evaluate very low-risk patients for pulmonary embolism exclusion.
Highlights
- Calculates the PERC score using eight validated clinical criteria.
- Assesses age, heart rate, oxygen saturation, and key risk factors.
- Identifies the number of positive pulmonary embolism criteria.
- Provides a clear PERC rule-out interpretation for low-risk patients.
- Supports rapid bedside assessment of suspected pulmonary embolism.
Table of Contents
How PERC Calculator - Pulmonary Embolism Rule-Out Criteria Works?
The PERC Calculator applies the eight Pulmonary Embolism Rule-out Criteria to determine how many findings are positive. Each positive criterion contributes one point, while each absent or negative criterion contributes zero points.
The calculator counts a criterion as positive when the patient is aged 50 years or older, has a heart rate of 100 bpm or higher, has oxygen saturation below 95%, or answers “Yes” to unilateral leg swelling, hemoptysis, recent surgery or trauma requiring hospitalization within the previous four weeks, previous pulmonary embolism or deep vein thrombosis, or current estrogen use.
| PERC criterion | Positive when | Points |
|---|---|---|
| Age | Age is 50 years or older | 1 |
| Heart rate | Heart rate is 100 bpm or higher | 1 |
| Oxygen saturation | Oxygen saturation is below 95% | 1 |
| Unilateral leg swelling | Yes | 1 |
| Hemoptysis | Yes | 1 |
| Recent surgery or trauma | Yes, requiring hospitalization within the previous four weeks | 1 |
| Previous PE or DVT | Yes | 1 |
| Estrogen use | Yes, including contraceptives, hormone therapy, or pregnancy-related exposure | 1 |
The maximum score is eight points. A score of zero means that none of the eight criteria is positive and corresponds to a PERC-negative result when the clinician has already determined that the patient has a low clinical pretest probability of pulmonary embolism. A score of one or more indicates that at least one PERC criterion is present and that PERC alone does not rule out pulmonary embolism.
Practical Use Cases
Emergency physicians can use the calculator during the initial assessment of an adult patient with possible pulmonary embolism after establishing a low clinical pretest probability. The score helps document whether all eight PERC criteria are absent before deciding whether further testing is appropriate.
Urgent care clinicians can use the tool to organize key history, vital-sign, and examination findings in patients presenting with symptoms such as chest discomfort or shortness of breath. A positive criterion should prompt consideration of the broader diagnostic pathway rather than reliance on a PERC-negative classification.
Primary care clinicians can use the calculator as a structured checklist when evaluating patients with possible venous thromboembolism symptoms and determining whether urgent emergency assessment is needed.
Medical students and trainees can use the calculator to learn the eight PERC criteria, the one-point-per-positive-finding scoring method, and the importance of applying PERC only after low pretest probability has been established.
Clinical researchers and educators can use the calculator to demonstrate how binary clinical findings are aggregated into a rule-out score and to support teaching about appropriate versus inappropriate use of decision rules.
Accuracy and Limitations
The calculator accurately counts the eight programmed criteria using the supplied thresholds: age 50 years or older, heart rate 100 bpm or higher, oxygen saturation below 95%, and affirmative responses for the five clinical history or examination criteria. Its interpretation is limited to identifying a PERC-negative result when the patient has a genuinely low clinical pretest probability of pulmonary embolism; it is not a standalone diagnostic test and should not be used to rule out pulmonary embolism in moderate- or high-risk patients. Results may also be affected by inaccurate vital signs, unclear timing of surgery or trauma, incomplete medical history, or differing clinical definitions of estrogen exposure and unilateral swelling. The calculator does not account for other risk factors, alternative diagnoses, clinician gestalt, or local diagnostic protocols.
Quick Examples
Example #1: PERC-Negative Low-Risk Patient
Example of a young patient with no positive PERC criteria, supporting pulmonary embolism rule-out when the clinical pretest risk is low.
Example #2: Tachycardia and Estrogen Use
Example of a patient with two positive PERC criteria due to an elevated heart rate and current estrogen use.
Example #3: Multiple Positive PERC Criteria
Example of an older patient with hypoxemia, tachycardia, unilateral leg swelling, and previous venous thromboembolism history.
