What is the initial test to evaluate for pulmonary embolism (PE) in a patient with suspected PE?

Initial Test to Evaluate for Pulmonary Embolism

The first step is to assess pretest probability using a validated clinical prediction rule (Wells score or revised Geneva score), then apply the Pulmonary Embolism Rule-Out Criteria (PERC) for low-risk patients or obtain high-sensitivity D-dimer testing—not imaging—as the initial diagnostic test for low and intermediate probability patients. 1

Step 1: Pretest Probability Assessment

Before ordering any test, you must stratify the patient's risk using one of these validated approaches:

• Wells score or revised Geneva score are equally accurate and should be used to categorize patients into low (10% PE prevalence), intermediate (30%), or high (~65%) probability groups 1, 2
• Clinical gestalt by experienced clinicians performs equally well as formal prediction rules, with sensitivity of 97% and specificity of 22%, though structured tools help standardize evaluation for less experienced clinicians 1, 3
• The Wells score includes: clinical signs of DVT (3 points), PE as likely as alternative diagnosis (3 points), heart rate >100 bpm (1.5 points), immobilization/surgery (1.5 points), previous PE/DVT (1.5 points), hemoptysis (1 point), and malignancy (1 point) 1, 4

Step 2: Apply PERC for Low-Risk Patients

For patients with low pretest probability, apply all 8 PERC criteria before ordering any tests:

• Age <50 years, pulse <100 bpm, oxygen saturation ≥95%, no hemoptysis, no estrogen use, no prior VTE, no recent surgery/trauma within 4 weeks, and no unilateral leg swelling 1, 3, 5
• If all 8 PERC criteria are met, stop—no further testing is needed 1, 3
• PERC has a miss rate of only 0.3% when properly applied and avoids 22% of unnecessary D-dimer tests 3, 5

Critical pitfall: PERC should never be applied to intermediate or high-risk patients—it is only for low pretest probability patients 3, 5

Step 3: High-Sensitivity D-Dimer Testing

D-dimer is the initial diagnostic test for:

• Low pretest probability patients who do not meet all PERC criteria 1
• All intermediate pretest probability patients 1

D-dimer interpretation:

• For patients ≤50 years: use standard cutoff of <500 ng/mL 4
• For patients >50 years: use age-adjusted cutoff (age × 10 ng/mL), which increases the proportion of patients in whom PE can be excluded from 6.4% to 30% without additional false-negative findings 1, 4
• Only high-sensitivity D-dimer assays (ELISA or turbidimetric) should be used, with sensitivity of 96% and specificity of 35% 1, 3

If D-dimer is below the appropriate threshold, PE is excluded—no imaging is needed 1, 6

Step 4: Imaging for High Pretest Probability

For high pretest probability patients, proceed directly to CT pulmonary angiography (CTPA) without D-dimer testing:

• A negative D-dimer cannot safely exclude PE in high-probability patients, so skip D-dimer entirely and go straight to imaging 1, 3
• CTPA has sensitivity >95% for segmental or larger emboli and is the primary imaging modality for hemodynamically stable patients 3, 7
• Reserve ventilation-perfusion (V/Q) scans for patients with contraindication to CTPA or when CTPA is unavailable 1, 3

Important Caveats

D-dimer in hospitalized patients: D-dimer specificity is lower in inpatients due to comorbidities, recent surgery, infection, and inflammation—fewer than 10% of hospitalized patients will have a negative D-dimer. However, testing remains appropriate because sensitivity stays high, and a normal level combined with appropriate risk stratification can still prevent unnecessary imaging 1, 3, 4

Never order D-dimer as a screening test: D-dimer should only be ordered after pretest probability assessment, not indiscriminately for all patients with respiratory symptoms 3, 4

Imaging is never the initial test for low or intermediate probability patients—this approach leads to overdiagnosis, unnecessary radiation exposure, and false-positive results 1