What is the likelihood of a pulmonary embolism (PE) in a patient with a positive D-dimer (1.39 μg/mL FEU), normal oxygen saturation (SaO2 98% on room air), normotension (blood pressure 111/65 mmHg), normal heart rate (HR 74 beats per minute), normal respiratory rate (RR 16 breaths per minute), and normal body temperature (36.3 degrees Celsius)?

Likelihood of Pulmonary Embolism with Positive D-dimer

A positive D-dimer of 1.39 μg/mL FEU in isolation cannot confirm or exclude PE, as D-dimer has poor positive predictive value and must be interpreted in the context of clinical probability—your next step is to calculate a Wells or Geneva score to determine pretest probability, then proceed to CT pulmonary angiography (CTPA) if the score indicates intermediate or high probability. 1

Understanding D-dimer Limitations

The positive D-dimer result you have does not establish a diagnosis of PE. D-dimer testing has high negative predictive value but very low positive predictive value—it is useful only for ruling out PE, not confirming it. 1 The specificity of D-dimer is poor, meaning many conditions besides PE cause elevation, including cancer, hospitalization, infection, inflammation, and pregnancy. 1

Clinical Probability Assessment is Mandatory

Your patient's vital signs are reassuring (normal oxygen saturation 98%, normal heart rate 74 bpm, normal blood pressure, normal respiratory rate, normal temperature), which suggests they may have low clinical probability. However, you must formally calculate either a Wells score or revised Geneva score to stratify pretest probability before determining the likelihood of PE. 1, 2

Key Clinical Variables to Assess

For the revised Geneva score, assign points for: 1

• Previous PE or DVT (1 point simplified version)
• Heart rate 75-94 bpm (1 point) or ≥95 bpm (2 points)—your patient has HR 74, so 0 points
• Recent surgery or fracture within past month (1 point)
• Hemoptysis (1 point)
• Active cancer (1 point)
• Unilateral lower-limb pain (1 point)
• Pain on deep venous palpation with unilateral edema (1 point)
• Age >65 years (1 point)

Interpreting Clinical Probability

Regardless of which score you use, the proportion of patients with confirmed PE is approximately 10% in low-probability, 30% in intermediate-probability, and 65% in high-probability categories. 1 Using the two-level classification, PE prevalence is 12% in PE-unlikely and 30% in PE-likely categories. 1

Your Patient's PERC Status

Your patient fails PERC criteria because they do not meet all eight required criteria—specifically, the positive D-dimer itself indicates PERC cannot be applied retrospectively. 1, 2 PERC is designed to avoid D-dimer testing altogether in very low-risk patients, not to interpret results after testing. 1, 2

Next Steps Based on Clinical Probability

If Low or Intermediate Clinical Probability

With a positive D-dimer and low-to-intermediate clinical probability, proceed directly to CTPA, which has sensitivity of 83% and specificity of 96%. 1, 2 The elevated D-dimer (1.39 μg/mL is above the standard 0.5 μg/mL cutoff) mandates imaging in this context. 1

If High Clinical Probability

If your clinical assessment yields high probability, proceed immediately to CTPA without relying on the D-dimer result, as imaging is required regardless. 2, 3 In high-probability patients, even a negative D-dimer would not obviate the need for imaging. 2, 3

Age-Adjusted D-dimer Consideration

If your patient is >50 years old, note that age-adjusted D-dimer cutoffs (age × 10 ng/mL) improve specificity while maintaining sensitivity >97%. 1, 3 However, since your patient's D-dimer of 1390 ng/mL (1.39 μg/mL FEU) would exceed even an age-adjusted cutoff for patients up to age 139, this distinction is academic in this case—the D-dimer is definitively elevated. 3

Critical Pitfalls to Avoid

• Do not use D-dimer alone to estimate PE likelihood—it requires clinical probability assessment for interpretation. 1
• Do not assume normal vital signs exclude PE—approximately 30% of patients with intermediate clinical probability have PE despite reassuring vital signs. 1
• Do not delay imaging while waiting for additional tests if clinical probability is intermediate or high with positive D-dimer. 2
• Do not assume the patient is low-risk based solely on normal oxygen saturation—PE can be present with normal SaO2, especially in younger patients without underlying cardiopulmonary disease. 1

Quantifying the Actual Likelihood

Without knowing your patient's complete clinical picture (history of prior VTE, recent surgery, cancer status, leg symptoms, hemoptysis), the likelihood of PE ranges from 12% (if PE-unlikely by formal scoring) to 30% (if PE-likely) to potentially 65% (if high clinical probability). 1 The normal vital signs and oxygen saturation suggest lower probability, but formal scoring is essential. 1, 2