From the Guidelines
A D-dimer test is not always necessary when getting an ultrasound for unilateral lower extremity edema, but it can be a valuable complementary test in certain clinical scenarios. The primary diagnostic tool for suspected deep vein thrombosis (DVT) is the compression ultrasound, which directly visualizes clots in the veins. D-dimer testing is most useful as an initial screening tool before imaging, particularly in patients with low to moderate clinical probability of DVT, as suggested by the American Society of Hematology 2018 guidelines for management of venous thromboembolism: diagnosis of venous thromboembolism 1. A negative D-dimer in these patients can safely rule out DVT without proceeding to ultrasound. However, if clinical suspicion is high or if an ultrasound has already been ordered based on symptoms and risk factors, the D-dimer may provide limited additional value.
Key Considerations
- D-dimer has high sensitivity (about 95%) but poor specificity, meaning it's often elevated in many non-DVT conditions including infection, inflammation, cancer, pregnancy, and advanced age 1.
- The ASH guideline panel recommends 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.
- In practice, if a patient presents with unilateral leg swelling and the healthcare provider has already determined an ultrasound is necessary, they may choose to skip the D-dimer test and proceed directly to imaging, especially if the clinical suspicion for DVT is high or if the patient has conditions that would likely cause a false-positive D-dimer result 1.
Clinical Decision Making
- The decision to use D-dimer testing should be based on the individual patient's clinical presentation, risk factors, and the pre-test probability of DVT.
- For patients with low to moderate clinical probability of DVT, a negative D-dimer can safely rule out DVT, while a positive D-dimer should be followed by ultrasound to confirm the diagnosis.
- For patients with high clinical suspicion of DVT or those with conditions that would likely cause a false-positive D-dimer result, proceeding directly to ultrasound may be the most appropriate course of action.
From the Research
Unilateral Lower Extremity Edema and D-Dimer Testing
- Unilateral lower extremity edema can be caused by various conditions, including deep vein thrombosis (DVT), venous insufficiency, lymphedema, and lipedema 2.
- The diagnosis of DVT requires a multifaceted approach, including clinical assessment, evaluation of pre-test probability, and objective diagnostic testing, such as D-dimer testing and compression ultrasound 3.
Role of D-Dimer Testing
- D-dimer testing is commonly used to diagnose DVT, with a high negative predictive value, which can help reduce the need for imaging 3, 4.
- However, small thrombi may be associated with low D-dimer levels, increasing false negatives, particularly in cases of isolated distal DVT (IDDVT) 4.
- The administration of empiric anticoagulation therapy, such as rivaroxaban, may reduce the sensitivity and increase false negative results of D-dimer testing 5.
Diagnostic Approach
- For patients with acute unilateral lower-extremity edema, immediate evaluation for DVT with a D-dimer test or compression ultrasonography is recommended 6.
- If DVT is suspected, a clinical decision rule can be used to stratify the pre-test probability, and D-dimer testing can be used to rule out DVT if the pre-test probability is low 3.
- Compression ultrasonography is recommended if the D-dimer test is positive or if the pre-test probability is high 3.
Considerations
- The diagnostic approach should take into account the patient's medical history, physical examination, and other diagnostic tests, such as duplex ultrasonography and lymphoscintigraphy, to determine the underlying cause of edema 2, 6.
- Treatment of edema should be specific to the underlying cause, and may include diuretics, compression therapy, and other interventions 6.