From the Guidelines
The D-dimer test is primarily used to help rule out deep vein thrombosis (DVT), pulmonary embolism (PE), and other blood clotting disorders, with a negative result being highly reliable for exclusion in patients with low to moderate clinical probability. The test measures the presence of D-dimer, a protein fragment produced when a blood clot dissolves in the body. A negative D-dimer result (below the threshold value, typically 500 ng/mL FEU) is highly reliable for excluding DVT or PE in patients with low to moderate clinical probability, often eliminating the need for further imaging tests 1. However, a positive D-dimer result is not specific to blood clots and requires additional diagnostic testing, as elevated levels can occur in many conditions including pregnancy, inflammation, cancer, surgery, trauma, and advanced age.
Some key points to consider when using the D-dimer test include:
- The test's primary value is in its negative predictive power, helping clinicians confidently rule out dangerous clotting conditions without subjecting patients to unnecessary radiation or invasive procedures.
- D-dimer levels will be elevated with any significant thrombotic process, so this test is of limited value in pregnant, postoperative, and trauma patients, as well as in patients determined to be at high risk of PE by validated clinical criteria 1.
- The specificity and sensitivity of the D-dimer assay can vary based on the diagnostic purpose and the type of test used, with an overall estimated sensitivity and specificity of 90.5% and 54.7%, respectively, in patients with suspected DVT 1.
- The reporting units for D-dimer results can be inconsistent, with some laboratories using fibrinogen equivalent units (FEU) and others using D-dimer units (DDU), which can lead to confusion among non-laboratory healthcare personnel 1.
Overall, the D-dimer test is a useful tool for ruling out DVT and PE in patients with low to moderate clinical probability, but its results must be interpreted in the context of the patient's overall clinical presentation and other diagnostic findings.
From the Research
D-Dimer Test Overview
- The D-Dimer test is used to diagnose and rule out Deep Vein Thrombosis (DVT) and Pulmonary Embolism (PE) 2, 3, 4, 5, 6
- It measures the levels of D-Dimer, a protein fragment produced when a blood clot breaks down 2, 5
Diagnostic Uses
- The test is particularly useful in the outpatient population referred to the emergency department because of suspected DVT or PE 2
- It can be used as a stand-alone test to rule out DVT, reducing the need for ultrasounds and other imaging tests 3
- In primary care settings, point-of-care testing for D-Dimer can help diagnose VTE and reduce referrals to hospitals for imaging confirmatory investigations 4
Test Characteristics
- The test has high sensitivity, but poor specificity, making it useful for ruling out VTE, but not for confirming the diagnosis 2, 6
- A negative D-Dimer test result can be used to rule out PE in patients with a low pre-test probability 6
- The test's negative predictive value is high, making it a useful tool for excluding VTE diagnosis 5
Clinical Applications
- The test can be used in combination with clinical decision rules and imaging techniques to diagnose VTE 2
- It can be used to monitor patients with suspected recurrent VTE or those with limited thrombus burden 2
- The test's results should be interpreted in the context of the patient's clinical presentation and other diagnostic findings 2, 6