Is a D-dimer (D-dimer test) level of 319.0 ng/mL significant?

Is a D-dimer of 319.0 ng/mL Significant?

A D-dimer level of 319.0 ng/mL is below the standard diagnostic threshold of 500 ng/mL and is considered normal, effectively ruling out acute venous thromboembolism and aortic dissection in patients with low-to-intermediate clinical probability. 1, 2

Understanding the Threshold

• The standard cutoff for D-dimer elevation is 500 ng/mL (0.5 μg/mL), with values below this threshold considered normal and having excellent negative predictive value for excluding thrombotic conditions 1, 3

• Your level of 319 ng/mL falls well below this threshold, representing approximately 64% of the upper limit of normal 2

• For acute aortic dissection, D-dimer levels >500 ng/mL have a sensitivity of 94-100%, meaning a level of 319 ng/mL makes this diagnosis extremely unlikely 1, 2

• For pulmonary embolism, a D-dimer below 500 ng/mL has a negative predictive value of 99%, allowing safe exclusion of PE in outpatients with suspected disease 3

Clinical Implications of Your Result

• This level effectively excludes acute pulmonary embolism in patients with low or intermediate clinical probability, with only a 1% risk of thromboembolic events during follow-up when anticoagulation is withheld 3

• Acute aortic dissection is essentially ruled out with this level, as D-dimer is typically immediately and markedly elevated in this condition 1, 2

• Deep vein thrombosis is highly unlikely with this normal result 2

• No further diagnostic imaging (CT angiography, compression ultrasonography) is needed for venous thromboembolism if clinical probability is low-to-intermediate 2

Important Context-Specific Considerations

• Age matters for interpretation: If you are over 50 years old, an age-adjusted cutoff (age × 10 ng/mL) can be used, which would make your threshold even higher and your result even more reassuring 2

• Pregnancy has different reference ranges: D-dimer levels increase progressively during pregnancy, with normal ranges of 110-400 ng/mL in the first trimester, 140-750 ng/mL in the second trimester, and 160-1,300 ng/mL in the third trimester 1, 2

  • Your level of 319 ng/mL would be normal even in pregnancy across all trimesters 1

• COVID-19 context: In COVID-19 patients, D-dimer >2,120 ng/mL was associated with mortality, making your level of 319 ng/mL reassuring in this context 1, 2

Critical Pitfall to Avoid

• Verify the reporting units with your laboratory: D-dimer can be reported in Fibrinogen Equivalent Units (FEU) or D-dimer Units (DDU), with FEU being approximately two-fold higher than DDU 2
  • If your result is reported in FEU, it would be equivalent to approximately 160 ng/mL in DDU units, making it even more clearly normal 2
  • Always confirm the reference range specific to your laboratory's assay method 2

When This Normal Result Still Requires Caution

• If clinical suspicion for PE or aortic dissection is high (not low-to-intermediate), proceed directly to imaging regardless of D-dimer level 2

• D-dimer is a rule-out test, not a rule-in test—it cannot diagnose thrombotic disease, only help exclude it when normal 2, 4