What is the best course of action for an elderly female patient with a positive D-dimer (D-dimer test), normal vital signs, and no other specified comorbidities or symptoms, suspected of having a pulmonary embolism (PE)?

Management of Elderly Female Patient with Positive D-Dimer and Suspected PE

In this elderly female patient with a positive D-dimer, you must proceed directly to CT pulmonary angiography (CTPA) to confirm or exclude pulmonary embolism, as the elevated D-dimer above the age-adjusted threshold mandates imaging regardless of pretest probability. 1

Critical First Step: Interpret the D-Dimer Using Age-Adjusted Threshold

• For patients over 50 years old, the D-dimer threshold should be calculated as age × 10 ng/mL, not the standard 500 ng/mL cutoff 1, 2
• If this patient's D-dimer exceeds her age-adjusted threshold (e.g., if she is 70 years old, the threshold would be 700 ng/mL), imaging is mandatory 1, 2
• The age-adjusted approach is essential because standard D-dimer specificity drops dramatically with age—falling to only 10% in patients over 80 years—leading to excessive false positives if the 500 ng/mL cutoff is used 2

Immediate Diagnostic Pathway

• Order CTPA immediately as the definitive diagnostic test 1
• Do not delay imaging to reassess clinical probability or order additional laboratory tests, as an elevated D-dimer (above age-adjusted threshold) has already triggered the need for imaging 1
• Reserve ventilation-perfusion scanning only if CTPA is contraindicated (e.g., severe contrast allergy, significant renal impairment) or unavailable 1

Common Pitfalls to Avoid in Elderly Patients

• Do not apply the Pulmonary Embolism Rule-Out Criteria (PERC) to this patient, as PERC requires age <50 years as one of its eight mandatory criteria 2
• Do not use the standard 500 ng/mL D-dimer cutoff for decision-making in elderly patients, as this leads to unnecessary imaging due to poor specificity 2
• Do not withhold imaging based on "low clinical suspicion" once the age-adjusted D-dimer is elevated—the test has already stratified her into the imaging-required category 1, 3

If PE is Confirmed on CTPA

• Assess hemodynamic stability immediately 4
• For hemodynamically stable patients, initiate anticoagulation with rivaroxaban 15 mg twice daily for 21 days, then 20 mg once daily 4
• Do not use rivaroxaban if the patient is hemodynamically unstable or may require thrombolysis—use unfractionated heparin instead 4
• Check renal function: if CrCl is 15-30 mL/min, observe closely for bleeding; if CrCl <15 mL/min, avoid rivaroxaban entirely 4

If PE is Excluded on CTPA

• No anticoagulation is needed 1
• Investigate alternative diagnoses for her presenting symptoms 1
• The negative predictive value of CTPA is sufficiently high that no further testing for PE is required 1

Special Consideration: What If D-Dimer Was Below Age-Adjusted Threshold?

• If the D-dimer had been below the age-adjusted threshold (age × 10 ng/mL), no imaging would be necessary, and PE could be safely excluded 1, 2
• This approach has a negative predictive value of 99.5% when properly applied 5
• However, since you stated the D-dimer is positive, this scenario does not apply 1