Is a D-dimer (Deep Vein Thrombosis/Pulmonary Embolism biomarker) result of 1.08 mg/L FEU (Fibrin Equivalent Units) normal?

D-Dimer Interpretation for Venous Thromboembolism

A D-dimer value of 1.08 mg/L FEU is elevated above the standard reference range (0.00-0.49 mg/L FEU) and requires further evaluation, but may be normal if age-adjusted thresholds are applied in patients over 50 years old.

Understanding D-dimer Values and Age Adjustment

D-dimer is a fibrin degradation product that serves as a biomarker for active coagulation and fibrinolysis. The interpretation of D-dimer results depends on several factors:

Standard vs. Age-Adjusted Thresholds

• Standard threshold: 0.50 mg/L FEU
• Age-adjusted threshold: For patients >50 years, the formula is age/100 mg/L FEU 1
  • Example: 60-year-old patient would have a cut-off of 0.60 mg/L FEU
  • Example: 80-year-old patient would have a cut-off of 0.80 mg/L FEU

Clinical Application

• For patients >50 years old, the age-adjusted threshold should be used to improve specificity while maintaining high sensitivity 1
• For a patient who is:
  • Under 50: The value of 1.08 mg/L FEU is abnormal
  • 60 years old: The value is still abnormal (above 0.60 mg/L FEU)
  • 80 years old: The value is still abnormal (above 0.80 mg/L FEU)
  • 110 years old: The value would be normal (below 1.10 mg/L FEU)

Clinical Significance and Next Steps

Diagnostic Value

• D-dimer has high sensitivity (90.5%) but low specificity (54.7%) for DVT/PE 1
• A negative D-dimer result in a highly sensitive assay safely excludes PE in patients with low or moderate clinical probability 1
• The value of 1.08 mg/L FEU is more than twice the standard cut-off, suggesting increased risk

Risk Stratification

• D-dimer values should always be interpreted in conjunction with clinical probability assessment (e.g., Wells score) 1
• Extremely elevated D-dimer values (>5000 μg/L) are highly specific for serious conditions including VTE, sepsis, and/or cancer 2

Important Considerations

Assay Variability

• D-dimer can be reported in different units:
  • Fibrinogen Equivalent Units (FEU)
  • D-dimer Units (DDU) - approximately half the value of FEU 1, 3
• Different assays have different sensitivities and specificities 1
• Results are not transferable between methods or institutions 1

False Positives

D-dimer levels can be elevated in numerous conditions besides VTE:

• Advanced age
• Pregnancy
• Recent surgery
• Cancer
• Infections (including COVID-19)
• Inflammatory conditions
• Hospitalized patients 1, 4

Algorithm for Clinical Decision Making

1. Determine patient's age:

   • If >50 years, calculate age-adjusted threshold (age/100)
   • Compare D-dimer value to appropriate threshold

2. Assess clinical probability (using validated tools like Wells score):

   • Low probability + elevated D-dimer: Imaging recommended
   • Moderate probability + elevated D-dimer: Imaging recommended
   • High probability: Proceed directly to imaging regardless of D-dimer

3. For this specific value (1.08 mg/L FEU):

   • For patients under 108 years old: Consider abnormal
   • Proceed with appropriate imaging studies (CT pulmonary angiography for PE or compression ultrasonography for DVT)

Conclusion

The D-dimer value of 1.08 mg/L FEU is elevated above the standard reference range and would be considered abnormal for most patients, even when using age-adjusted thresholds for patients under 108 years old. Further diagnostic evaluation with appropriate imaging is warranted based on clinical probability assessment.