From the Guidelines
The initial blood test for diagnosing Deep Vein Thrombosis (DVT) is the D-dimer test. This test measures the levels of D-dimer, a protein fragment produced when a blood clot dissolves in the body. A negative D-dimer test can effectively rule out DVT in patients with low to moderate clinical probability, making it a valuable initial screening tool 1. However, it's essential to understand that while a negative D-dimer test is helpful in excluding DVT, a positive result is not specific to DVT and requires further investigation. D-dimer levels can be elevated in many conditions, including pregnancy, recent surgery, infection, cancer, and advanced age.
Some key points to consider when using the D-dimer test for DVT diagnosis include:
- The test is most useful when combined with clinical assessment tools like the Wells score to determine the pre-test probability of DVT, which helps guide the diagnostic approach and interpretation of test results 1.
- A study published in the Journal of Thrombosis and Haemostasis in 2017 noted that the combination of pretest probability assessment, D-dimer testing, and compression ultrasound is the recommended approach for diagnosing suspected first DVT 1.
- It's crucial to consider the disease prevalence and diagnostic failure rate when interpreting D-dimer test results, as the threshold for suspecting DVT and initiating diagnostic testing has lowered over the past few years, leading to a decrease in DVT prevalence in examined patients 1.
Overall, the D-dimer test is a useful initial screening tool for DVT, but it should be used in conjunction with clinical assessment and other diagnostic imaging techniques to confirm the diagnosis. The D-dimer test is recommended as the initial blood test for diagnosing DVT, especially in patients with low to moderate clinical probability.
From the Research
Initial Blood Test for Diagnosing Deep Vein Thrombosis (DVT)
The initial blood test for diagnosing DVT is the D-dimer test.
- This test is used to assess the pre-test probability of DVT, which can be classified as "unlikely" or "likely" 2, 3, 4.
- If DVT is considered "unlikely", a D-dimer test is performed, and if the result is normal, DVT can be excluded 2, 3, 4.
- The D-dimer test measures the level of D-dimer in the blood, which is a protein fragment produced when blood clots are broken down 3, 4.
- A negative D-dimer result can help rule out DVT, while a positive result may indicate the presence of a blood clot and require further testing, such as compression ultrasound 2, 3, 4.
Factors Affecting D-dimer Test Results
Certain factors can affect the accuracy of D-dimer test results, including:
- Empiric anticoagulation therapy, such as rivaroxaban, which can reduce the sensitivity of the D-dimer test and increase false negative results 5.
- The timing of the D-dimer test, which should be performed before the administration of anticoagulant therapy 5.
Clinical Decision Rules for DVT Diagnosis
Clinical decision rules, such as the Wells score, can be used in combination with D-dimer testing to diagnose DVT 2, 3, 4, 6.
- These rules assess clinical symptoms and signs, such as calf swelling and DVT as the most likely diagnosis, to determine the pre-test probability of DVT 6.
- A simplified decision rule has been proposed, which uses two variables, calf swelling and DVT as the most likely diagnosis, to define low and high clinical pretest probability groups 6.