Is a computed tomography pulmonary angiogram (CTPA) justified in a patient over 50 years old with a mildly elevated d-dimer (D-dimer) level but no clear clinical suspicion of pulmonary embolism (PE)?

CTPA is Not Justified for Mildly Elevated D-dimer Without Clinical Suspicion of PE

CTPA should not be requested solely based on a mildly elevated D-dimer value of 1.2 mg/L in a patient over 50 years old without clinical suspicion of pulmonary embolism, as this value falls below the age-adjusted threshold and does not warrant further imaging. 1

Clinical Decision-Making Algorithm for Suspected PE

Step 1: Assess Clinical Probability

• Use validated clinical prediction rules (Wells score, revised Geneva score) to estimate pretest probability of PE 1, 2
• For patients with no clinical suspicion of PE, a low clinical probability should be assigned 1
• Clinical judgment remains essential in determining the likelihood of PE 1

Step 2: Apply Age-Adjusted D-dimer Interpretation

• For patients over 50 years old, the recommended age-adjusted D-dimer cutoff is age × 10 ng/mL (or μg/L) 1
• For this patient over 50 years old, the age-adjusted cutoff would be at least 500 μg/L (0.5 mg/L) 1
• With a D-dimer of 1.2 mg/L and age over 50, this value must be compared to the age-adjusted threshold 1, 3
• For example, if the patient is 70 years old, the age-adjusted threshold would be 700 μg/L (0.7 mg/L) 1, 2

Step 3: Determine Need for Imaging

• CTPA is recommended only for patients with high clinical probability or those with positive D-dimer above the age-adjusted threshold 1
• Imaging is not warranted in patients with low clinical probability and D-dimer below the age-adjusted cutoff 1
• The European Society of Cardiology explicitly recommends against imaging studies in patients with D-dimer levels below the age-adjusted cutoff 1

Evidence Supporting This Approach

D-dimer Testing in Older Patients

• Standard D-dimer cutoff (500 μg/L) has decreased specificity in older patients, leading to unnecessary imaging 1, 3
• Age-adjusted D-dimer thresholds maintain high sensitivity (>97%) while significantly improving specificity in patients over 50 years 1, 2
• The American College of Physicians strongly recommends using age-adjusted D-dimer thresholds for patients older than 50 years 1

Avoiding Unnecessary CTPA

• CTPA should not be the initial test in patients with low or intermediate pretest probability 1
• Performing CTPA without appropriate clinical indication leads to unnecessary radiation exposure and potential contrast-related complications 1, 2
• The negative predictive value of a normal D-dimer (using appropriate thresholds) is very high (>99%) in patients with low clinical probability 4, 5

Common Pitfalls to Avoid

Overreliance on D-dimer Testing

• D-dimer should not be used as a screening test in patients without clinical suspicion of PE 1
• Positive D-dimer alone is insufficient to diagnose PE and should not automatically trigger imaging 1, 2
• D-dimer has low specificity and can be elevated in many conditions including infection, inflammation, cancer, and pregnancy 1, 2

Failure to Apply Age-Adjusted Thresholds

• Not adjusting D-dimer thresholds for age leads to overdiagnosis and unnecessary imaging in older patients 1, 2
• For this patient with a D-dimer of 1.2 mg/L, the age-adjusted threshold must be calculated before deciding on CTPA 1, 3
• If the patient's age is 70, the threshold would be 0.7 mg/L, and CTPA would be indicated; if the patient is 120 years old, the threshold would be 1.2 mg/L, and CTPA might not be indicated 1

Inappropriate Use of PERC Rule

• The PERC rule is only applicable to patients with low clinical probability 1
• While this patient does not meet PERC criteria (age >50), this alone is not sufficient reason to proceed to CTPA without considering clinical probability and age-adjusted D-dimer 1, 2
• PERC was designed to identify patients at such low risk that D-dimer testing is unnecessary, not to determine need for CTPA 1

In conclusion, for a patient over 50 years with no clinical suspicion of PE and a mildly elevated D-dimer of 1.2 mg/L, CTPA is not justified if the D-dimer value falls below the age-adjusted threshold. This approach minimizes unnecessary radiation exposure and potential contrast-related complications while maintaining patient safety 1, 2.