Should a D-dimer test be repeated in a patient with a history of elevated D-dimer levels, active smoking status, and a negative Pulmonary Embolism Rule-out Criteria (PERC) score?

D-dimer Testing in a Patient with Previous Elevated Levels and Negative PERC Score

A D-dimer test is not recommended for this patient with a negative PERC score, despite previous elevated D-dimer levels and active smoking status.

Diagnostic Algorithm for Suspected VTE

Step 1: Assess Pre-test Probability

• The patient has a negative PERC score, indicating very low probability of PE
• PERC rule has excellent negative predictive value when all criteria are met
• Active smoking is a risk factor but alone doesn't warrant D-dimer testing when PERC is negative

Step 2: Determine Need for D-dimer Testing

• According to American College of Chest Physicians guidelines, patients with low pretest probability and negative PERC score do not require D-dimer testing 1
• The American Society of Hematology (ASH) recommends against additional testing following negative clinical assessment in low-risk patients 1

Step 3: Interpret Previous D-dimer Results

• Previous elevated D-dimer levels of unknown cause should be considered in context:
  • D-dimer has poor specificity (40-46%) and is elevated in many conditions 2
  • D-dimer can be elevated due to smoking, inflammation, and other non-thrombotic conditions
  • Without clinical symptoms or high pre-test probability, elevated D-dimer alone has limited diagnostic value

Important Considerations

D-dimer Testing Limitations

• D-dimer has excellent negative predictive value (>99%) but poor specificity 2
• False positive results are common, especially in:
  • Smokers
  • Older patients
  • Inflammatory conditions
  • Post-surgical states
  • Pregnancy
  • Cancer

When to Consider D-dimer Testing Despite Negative PERC

D-dimer would be indicated if:

• PERC criteria were not fully met
• Patient had moderate to high clinical probability of VTE
• Patient developed new symptoms suggesting VTE

Risk of Unnecessary Testing

• Following a negative D-dimer with imaging leads to:
  • Unnecessary radiation exposure
  • Potential contrast nephropathy
  • Healthcare costs
  • Patient anxiety
  • Incidental findings requiring further workup

Clinical Pitfalls to Avoid

1. Overreliance on D-dimer: Using D-dimer as a screening test in low-risk patients increases false positives and unnecessary imaging 1, 2

2. Ignoring clinical assessment: PERC score is designed to identify patients at such low risk that further testing is not warranted 3

3. Testing cascade: A positive D-dimer would likely lead to CT pulmonary angiography despite low clinical probability, exposing the patient to unnecessary radiation

4. Misinterpreting previous results: Prior elevated D-dimer without diagnosed VTE suggests non-thrombotic cause and doesn't increase current risk if PERC is negative

In conclusion, for this patient with a negative PERC score and previous elevated D-dimer of unknown cause, the evidence strongly supports withholding D-dimer testing, as it would not improve outcomes related to morbidity, mortality, or quality of life.