What tests to order for a patient with shortness of breath (SOB) and cough, and a history of pulmonary embolism (PE)?

Diagnostic Testing for SOB and Cough with History of PE

In a patient with shortness of breath and cough who has a prior history of pulmonary embolism, you must first assess pretest probability using a validated clinical decision rule (Wells or Geneva score), then proceed with D-dimer testing if low-to-intermediate risk, or proceed directly to CT pulmonary angiography if high risk. 1

Risk Stratification is Mandatory

• Use a validated clinical prediction rule (Wells criteria or Geneva score) to estimate pretest probability before ordering any tests 1
• The history of prior PE is a significant risk factor that increases pretest probability, but does not automatically mandate imaging 1
• Clinical gestalt alone is acceptable if you are experienced, but structured scoring is preferred 1

Testing Algorithm Based on Pretest Probability

Low Pretest Probability (<15%)

• Apply the Pulmonary Embolism Rule-Out Criteria (PERC) first 1
• If all 8 PERC criteria are met (age <50, HR <100, O2 sat >94%, no recent surgery/trauma, no prior VTE, no hemoptysis, no unilateral leg swelling, no estrogen use), no further testing is needed 1, 2
• If PERC criteria are NOT all met, obtain high-sensitivity D-dimer 1
• If D-dimer is normal (age-adjusted: age × 10 ng/mL for patients >50 years, or <500 ng/mL if younger), stop—no imaging needed 1
• If D-dimer is elevated, proceed to CT pulmonary angiography 1

Intermediate Pretest Probability (15-40%)

• Obtain high-sensitivity D-dimer as the initial test—do NOT start with imaging 1
• Use age-adjusted D-dimer thresholds (age × 10 ng/mL) in patients over 50 years to improve specificity while maintaining >97% sensitivity 1
• If D-dimer is below the age-adjusted cutoff, no imaging is indicated 1
• If D-dimer is elevated, proceed to CT pulmonary angiography 1

High Pretest Probability (>40%)

• Proceed directly to CT pulmonary angiography—this is the preferred imaging modality 1
• Do NOT obtain D-dimer in high-risk patients because a negative result will not obviate the need for imaging 1
• Reserve ventilation-perfusion (V/Q) scanning for patients with contraindications to CT (renal failure, contrast allergy, pregnancy) or if CT is unavailable 1

Additional Baseline Testing

While the diagnostic algorithm above is specific for PE, obtain these tests concurrently:

• Chest X-ray to evaluate for alternative diagnoses (pneumonia, effusion, pneumothorax) that could explain symptoms 1, 3
• Arterial blood gas if hypoxemia is suspected 3
• ECG to assess for tachycardia, right heart strain, or alternative cardiac causes 1, 3
• Complete blood count, renal function, liver function as baseline labs 1

Adjunctive Testing Considerations

• Lower extremity compression ultrasound (CUS) can be useful if CT is contraindicated (renal failure, contrast allergy, pregnancy), as finding proximal DVT is sufficient to warrant anticoagulation without further PE imaging 1
• CUS shows DVT in 30-50% of patients with PE 1
• Bedside echocardiography is indicated if the patient is hemodynamically unstable (systolic BP <90 mmHg) to assess for right ventricular dysfunction 1

Critical Pitfalls to Avoid

• Do not skip pretest probability assessment—ordering CT on everyone leads to overdiagnosis of clinically insignificant subsegmental PEs and unnecessary anticoagulation risks 1
• Do not obtain D-dimer in high-risk patients—it wastes time and a negative result doesn't change management 1
• Do not order imaging if D-dimer is normal in low/intermediate risk patients—this exposes patients to unnecessary radiation and contrast nephropathy risk 1
• Remember that prior PE history increases risk but doesn't automatically mean high pretest probability—still use validated scoring systems 1