From the Guidelines
D-dimer is a valuable diagnostic tool for deep vein thrombosis (DVT), but its utility is limited to ruling out DVT in patients with low clinical probability, as suggested by the American College of Radiology in 2018 1. The D-dimer test has excellent sensitivity, but its specificity is limited, making it most useful as a rule-out test when negative.
- A normal D-dimer level in a patient with low clinical probability effectively excludes DVT, eliminating the need for further imaging, as noted in the study by Wells et al 1.
- However, positive results require confirmation with ultrasound or other imaging studies since many conditions besides DVT can elevate D-dimer, including pregnancy, inflammation, cancer, recent surgery, and advanced age.
- Age-adjusted cutoffs (age × 10 ng/mL for patients over 50) improve specificity in older populations, as mentioned in the 2018 study 1. The D-dimer test works by measuring fibrin degradation products that form when the body breaks down blood clots, reflecting active coagulation and fibrinolysis processes in the body.
- Elevated levels of D-dimer, typically above 500 ng/mL FEU (fibrinogen equivalent units), suggest the presence of abnormal blood clots, but this should be interpreted with caution and in the context of clinical presentation and other diagnostic findings, as emphasized by the American College of Radiology 1.
From the Research
Value of D-Dimer in DVT
- The D-dimer test is a useful tool in diagnosing deep vein thrombosis (DVT) [(2,3,4,5,6)].
- A negative D-dimer result can be used to exclude DVT, especially in patients with a low pre-test probability [(2,5,6)].
- The sensitivity of D-dimer in diagnosing DVT is high, but it can be affected by the use of anticoagulants such as rivaroxaban 3.
- D-dimer as a stand-alone test may be safe for excluding proximal DVT and can reduce the proportion of required ultrasounds 2.
- Clinical decision rules, such as the Wells score, can be used in combination with D-dimer to assess the need for objective imaging to rule out DVT [(2,4,5)].
Diagnostic Performance of D-Dimer
- The diagnostic performance of D-dimer can be affected by the type of assay used and the cut-off value [(2,3,6)].
- A study found that the sensitivity of D-dimer decreased from 99.0% to 97.0% after the administration of rivaroxaban 3.
- Another study found that a negative D-dimer result had a failure rate of 1.8% in diagnosing DVT 2.
- The primary care rule and the Wells rule can be used in combination with D-dimer to safely rule out DVT in primary care patients 5.
Clinical Applications of D-Dimer
- D-dimer can be used as a rapid exclusion test in patients with suspected recurrent DVT 6.
- A negative D-dimer result can be used to withhold additional diagnostic testing and heparin treatment in patients with suspected recurrent DVT 6.
- D-dimer can be used in combination with clinical decision rules to reduce unnecessary referrals for compression ultrasonography [(2,5)].
- The use of D-dimer in diagnosing DVT can help reduce the risk of post-thrombotic syndrome and pulmonary embolism 4.