From the Guidelines
The D-dimer test is a valuable screening tool for diagnosing Deep Vein Thrombosis (DVT) and Pulmonary Embolism (PE), with its primary significance lying in its high sensitivity and negative predictive value, making it most useful for ruling out these conditions when levels are normal, as indicated by studies such as 1. D-dimer is a fibrin degradation product formed when blood clots break down, and elevated levels suggest active clot formation and dissolution in the body. A negative D-dimer test (typically less than 500 ng/mL, though thresholds may vary by laboratory and patient age) effectively excludes DVT or PE in patients with low to moderate clinical probability, often eliminating the need for further imaging studies, as noted in 1 and 1. However, D-dimer has limited specificity as levels can be elevated in many other conditions including infection, inflammation, cancer, pregnancy, recent surgery, and advanced age. Therefore, while a normal D-dimer can help rule out thrombosis, an elevated level requires additional diagnostic testing such as ultrasound for suspected DVT or CT pulmonary angiography for suspected PE to confirm the diagnosis. The test is most effective when combined with clinical probability assessment tools like the Wells score to guide diagnostic decision-making, as suggested by 1 and 1. Some studies, such as 1 and 1, have also explored the use of age-adjusted D-dimer cutoffs, which may help improve the specificity of the test, particularly in older patients. Overall, the D-dimer test is a useful tool in the diagnosis of DVT and PE, but its results should be interpreted in the context of clinical probability and other diagnostic tests, as recommended by 1.
Some key points to consider when interpreting D-dimer results include:
- A negative D-dimer test can effectively rule out DVT or PE in patients with low to moderate clinical probability.
- An elevated D-dimer level requires additional diagnostic testing to confirm the diagnosis.
- D-dimer has limited specificity and can be elevated in many other conditions.
- Age-adjusted D-dimer cutoffs may help improve the specificity of the test, particularly in older patients.
- The test is most effective when combined with clinical probability assessment tools like the Wells score to guide diagnostic decision-making.
From the Research
D-Dimer Test Significance
The D-dimer test is a laboratory assay used to diagnose and manage thrombosis-related clinical conditions, including Deep Vein Thrombosis (DVT) and Pulmonary Embolism (PE) 2.
D-Dimer Levels and Thrombosis
- A high D-dimer level indicates the presence of thrombus formation, but it is not exclusive to thrombosis, as many conditions unrelated to thrombosis can also cause high D-dimer concentrations 2.
- The plasma level of D-dimer is nearly always increased in the presence of acute pulmonary embolism (PE), making it a useful marker for excluding PE in outpatients with suspected PE 3.
- A normal D-dimer level (below a cutoff value of 500 micrograms/L) may allow the exclusion of PE, with a negative predictive value of 99% 3.
Clinical Applications of D-Dimer
- D-dimer can be used to exclude VTE in symptomatic outpatients, provided that it is used in combination with the pretest clinical probability 2.
- High concentrations of D-dimer are associated with an increased risk of recurrent VTE 2.
- D-dimer can be used as a fibrin-related degradation marker for the diagnosis and management of patients with disseminated intravascular coagulation (DIC) 2, 4.
- D-dimer testing is widely used in conjunction with clinical pretest probability (PTP) for VTE exclusion, with a sensitivity and negative predictive value of 100% for all PTP subgroups 5.
Limitations of D-Dimer Assay
- D-dimer elevation can occur in various clinical scenarios, such as age, pregnancy, and cancer, which can limit its specificity 4.
- Very high D-dimer levels are not exclusive to thromboembolic diseases (TEDs) and can also be seen in other conditions, such as massive bleeding, sepsis with DIC, and multiple traumatic injuries 6.