What is the significance of an elevated D-dimer (D-dimer) test?

From the Guidelines

D-dimer should not be used alone to diagnose deep vein thrombosis (DVT) or pulmonary embolism (PE), but a negative result can help rule out these conditions in patients with low clinical probability. The American Society of Hematology 2018 guidelines recommend 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. A highly sensitive D-dimer assay is required if the D-dimer strategy is followed, and a negative result can rule out PE, with no additional testing or anticoagulation required. However, D-dimer has limited utility in hospitalized patients and in certain patient populations, such as postsurgical or pregnant patients, due to the high frequency of positive results with standard thresholds.

Some key points to consider when using D-dimer include:

• The specificity of D-dimer decreases with age and may be as low as 10% in patients over 80 years old 1
• D-dimer is more frequently elevated in patients with cancer, hospitalized patients, and during pregnancy 1
• A negative D-dimer result in a highly sensitive assay safely excludes PE in patients with low or moderate clinical probability, while a moderately sensitive assay excludes PE only in patients with low clinical probability 1
• Compression ultrasonography and computed tomographic venography can be used to diagnose DVT, with a sensitivity over 90% for proximal DVT and a specificity of about 95% 1

In terms of diagnostic yield, the Vidas D-dimer assay has been shown to have a 3-month thromboembolic risk of less than 1% in patients with a low clinical probability who are left untreated 1. The Tinaquant and SimpliRED assays have also been studied, with a 3-month thromboembolic risk of less than 1% in patients with a low clinical probability who are left untreated. However, the safety of these assays for ruling out PE has not been established in the moderate clinical probability category. The use of D-dimer should be guided by clinical judgment, taking into account the patient's clinical probability, age, and other factors that may affect the test's specificity.

From the Research

D-Dimer Test

• The D-dimer test is used to diagnose deep vein thrombosis (DVT) and pulmonary embolism (PE) in patients with suspected venous thromboembolism 2.
• The test measures the levels of D-dimer, a protein fragment produced when blood clots are broken down 3.
• A high D-dimer level can indicate the presence of a blood clot, but it is not specific to DVT or PE and can be elevated in other conditions, such as recent surgery, trauma, or infection 2.

Diagnostic Performance

• The sensitivity of the D-dimer test can be affected by the administration of anticoagulants, such as rivaroxaban, which can reduce the sensitivity and increase false negative results 3.
• The test has a high negative predictive value, meaning that a negative result can rule out DVT or PE in low-risk patients 4, 5.
• The diagnostic performance of the D-dimer test can vary depending on the assay method used, with some studies suggesting that fibrin-equivalent units (FEUs) may perform better than D-dimer units (DDUs) 4.

Clinical Application

• The D-dimer test is often used in combination with clinical decision rules, such as the Wells score, to assess the need for objective imaging to rule out DVT 6.
• However, some studies suggest that the D-dimer test can be used as a stand-alone test to rule out DVT in outpatients with suspected DVT, potentially reducing the need for ultrasounds 5.
• The test can also be used to evaluate the prognosis of patients with sepsis or COVID-19, with high D-dimer levels potentially indicating a worse outcome 2.