Which criteria are used to assess the probability of pulmonary embolism?

• A. Wells criteria only
• B. PERC criteria only
• C. Wells and PERC criteria
• D. D-dimer criteria only

Answer: (C)

Determining how likely a pulmonary embolism is relies on clinical prediction rules that estimate pretest probability and guide testing. The Wells score assigns points for features such as signs of deep vein thrombosis, whether PE is more likely than an alternative diagnosis, heart rate, recent immobilization or surgery, prior DVT/PE, hemoptysis, and active cancer. Summing these points places a patient into risk categories that help decide the next step in evaluation.

The PERC rule is a quick, separate check used when the patient is judged to be at very low pretest probability. If all eight criteria are negative—no age over 50, no tachycardia, oxygen saturation at or above 95%, no unilateral leg swelling, no hemoptysis, no recent surgery or trauma, no prior DVT/PE, and no estrogen use—PE can be ruled out without further testing.

Using both together makes sense: use the Wells score to gauge overall probability, and if deemed low probability, apply the PERC rule to potentially rule out PE without D-dimer or imaging. D-dimer testing or imaging then follows as needed based on the combined assessment. The other options aren’t as comprehensive because relying on D-dimer alone doesn’t provide probability, and using only one rule (Wells or PERC) misses the safe-rule-out pathway that the combination enables.