From the Guidelines
The D-dimer result of <0.22 mg/L FEU is normal, as it falls below the reference range of <0.50 mg/L FEU, effectively ruling out conditions associated with abnormal blood clot formation such as deep vein thrombosis (DVT) or pulmonary embolism (PE) in patients with low to moderate clinical probability. This negative D-dimer test is supported by the American Society of Hematology 2018 guidelines, which state that a negative D-dimer rules out DVT and no additional testing or anticoagulation is required 1. D-dimer is a fibrin degradation product formed when the body breaks down blood clots. Low levels indicate that significant clotting activity is not occurring in the body. No specific treatment or follow-up is needed based solely on this normal result. However, if clinical symptoms suggestive of thrombosis persist despite this negative result, further diagnostic evaluation may still be warranted, as D-dimer has excellent sensitivity but limited specificity.
Some key points to consider:
- A negative D-dimer result has a high negative predictive value, making it a useful tool for ruling out DVT and PE in patients with low to moderate clinical probability 1.
- The specificity of D-dimer decreases with age and may be affected by other patient characteristics, such as cancer, hospitalization, or pregnancy 1.
- Compression ultrasonography and computed tomographic venography may be used as additional diagnostic tools in patients with suspected DVT or PE, but are not necessary in patients with a negative D-dimer result and low clinical probability 1.
- The American Society of Hematology 2018 guidelines recommend against using a positive D-dimer alone to diagnose DVT, and against additional testing following negative proximal or whole-leg ultrasound in a population with low prevalence/PTP (#10%) 1.
Overall, the normal D-dimer result provides reassurance that active clotting disorders are unlikely present at this time, and no further action is needed unless clinical symptoms persist.
From the Research
D-Dimer Test
- The D-dimer test is a global indicator of coagulation activation and fibrinolysis, and an indirect marker of thrombotic activity 2.
- It is used to exclude venous thromboembolism (VTE), predict future risk of VTE, and diagnose and monitor disseminated intravascular coagulation (DIC) 2.
Clinical Applications
- D-dimer testing is used in combination with medical history, physical examination, and pre-test probability models to facilitate efficient and cost-effective diagnosis of VTE 3.
- It is also used to tailor therapy to disease severity, with anticoagulation options including unfractionated heparin, low molecular weight heparin, fondaparinux, and direct oral anticoagulants (DOACs) 3.
- D-dimer levels are monitored during anticoagulant therapy, with significant decreases in levels indicating effective treatment 4, 5.
Diagnostic Thresholds
- A D-dimer level of less than 0.50 mg/L FEU is considered normal 2.
- In patients with COVID-19, a D-dimer level of less than 6494 ng/mL may exclude deep vein thrombosis (DVT) 6.
- Elevated D-dimer levels are associated with an increased risk of VTE and poor survival in patients with cancer 4.
Limitations and Variability
- Assay standardization remains problematic, and clinicians need to be aware of variability in D-dimer assay performance and the characteristics of their institution's test when making clinical decisions 2.
- Different studies have reported varying optimal cutoffs for D-dimer levels, highlighting the need for careful interpretation of results in clinical practice 6.