Is a D-dimer (D-dimer test) reasonable in a man admitted with Congestive Heart Failure (CHF) and pneumonia who is acutely short of breath?

D-dimer Testing in a Patient with CHF and Pneumonia Who is Acutely Short of Breath

D-dimer testing is not recommended in this patient with CHF and pneumonia as these conditions represent highly likely alternative diagnoses that would render D-dimer results uninterpretable and potentially lead to unnecessary imaging.

Rationale for Not Performing D-dimer Testing

Clinical Probability Assessment is Key

When evaluating patients with suspected pulmonary embolism (PE), clinical probability assessment is the essential first step before any testing is performed. In this case:

• The patient already has two established diagnoses (CHF and pneumonia) that fully explain the acute shortness of breath
• Both conditions are known to cause elevated D-dimer levels independently of PE

Guidelines on D-dimer Testing in This Scenario

Multiple guidelines specifically advise against D-dimer testing in this situation:

• The British Thoracic Society guidelines explicitly state that D-dimer should not be performed "where an alternative diagnosis is highly likely" 1
• The American College of Physicians' best practice advice similarly states that D-dimer is not a routine "screening" test and should only be considered where there is reasonable suspicion of PE 1
• The 2019 ESC guidelines reinforce that D-dimer testing should be used only after clinical probability assessment 1

Why D-dimer Would Be Problematic in This Patient

1. Poor Specificity: D-dimer has low specificity in hospitalized patients due to comorbidities 1
2. False Positives: Both CHF and pneumonia independently cause elevated D-dimer levels 2
3. Cascade of Unnecessary Testing: A positive D-dimer (which is highly likely in this patient regardless of PE status) would lead to CT pulmonary angiography with:
   • Radiation exposure
   • Contrast risks
   • Potential incidental findings requiring follow-up
   • Increased healthcare costs

Appropriate Diagnostic Approach

Instead of reflexively ordering a D-dimer test, the clinician should:

1. Reassess Clinical Probability: Determine if there are specific features suggesting PE beyond what would be expected from CHF and pneumonia

   • Risk factors for venous thromboembolism
   • Clinical features disproportionate to the known diagnoses
   • Failure to respond to appropriate treatment for CHF and pneumonia

2. If PE Suspicion Remains High: Proceed directly to imaging (CTPA) rather than D-dimer testing 1

3. If PE Suspicion is Low: Continue treating the established diagnoses without PE-specific testing

Common Pitfalls to Avoid

• Diagnostic momentum: Ordering D-dimer "just to be safe" when alternative diagnoses are established
• Failure to recognize D-dimer limitations: D-dimer has very poor specificity in hospitalized patients with inflammatory conditions
• Overreliance on testing: Remember that D-dimer is not a screening test but part of a diagnostic algorithm that begins with clinical assessment

By avoiding D-dimer testing in this patient with highly likely alternative diagnoses, you can prevent an unnecessary diagnostic cascade while still providing appropriate care for the established conditions.