From the Guidelines
D-dimer testing is a valuable screening tool for ruling out deep vein thrombosis (DVT) and pulmonary embolism (PE) due to its high sensitivity but low specificity. A negative D-dimer result (typically less than 500 ng/mL FEU) in patients with low or moderate clinical probability effectively excludes these conditions, eliminating the need for further imaging studies 1. However, a positive D-dimer result requires additional diagnostic testing, usually ultrasound for suspected DVT or CT pulmonary angiography for suspected PE. D-dimer levels naturally increase with age, so age-adjusted cutoffs (age × 10 ng/mL for patients over 50) may be more appropriate for older patients 1. D-dimer is a fibrin degradation product formed when cross-linked fibrin clots are broken down by plasmin, making it a marker of active clot formation and dissolution. While extremely useful as a rule-out test, D-dimer has limited value in hospitalized patients, pregnant women, post-surgical patients, and those with cancer or inflammation, as these conditions can elevate D-dimer levels independently of thrombosis 1.
Some key points to consider when using D-dimer testing include:
- The specificity of D-dimer tests can be affected by various factors, such as the type of test used and the clinical probability of DVT or PE 1.
- The use of age-adjusted D-dimer cutoffs can help improve the specificity of the test in older patients 1.
- D-dimer testing is not recommended for patients with a high pretest probability of PE, as it is unlikely to change the diagnosis or management of these patients 1.
- The Pulmonary Embolism Rule-Out Criteria (PERC) can be used to identify patients with a low pretest probability of PE, in whom D-dimer testing may not be necessary 1.
Overall, D-dimer testing is a useful tool for ruling out DVT and PE, but it should be used in conjunction with clinical judgment and other diagnostic tests to ensure accurate diagnosis and management of these conditions.
From the Research
Role of D-dimer in Diagnosing Deep Vein Thrombosis (DVT) or Pulmonary Embolism (PE)
- D-dimer is a reliable and sensitive index of fibrin deposition and stabilization, and its presence in plasma should be indicative of thrombus formation 2.
- D-dimer testing can be used to exclude VTE in symptomatic outpatients, provided that it is used in combination with the pretest clinical probability 3, 2.
- A normal D-dimer result can reliably exclude DVT in outpatients with a low pretest likelihood, but it is less accurate in patients with a high pretest likelihood 3.
- D-dimer testing is most useful in patients with a low pretest likelihood for PE, and it may reduce the need for lung scans in these patients 3.
Limitations of D-dimer Testing
- D-dimer concentrations can be high in many conditions unrelated to thrombosis, making its positive predictive value rather poor 2.
- The negative predictive value of a D-dimer test can be low in the early postinjury phase, and it should not be used to exclude DVT or PE in trauma patients within the first 4 days of admission 4.
- D-dimer levels can be affected by anticoagulation therapy, and caution should be used when interpreting results from patients on these therapies 5.
Clinical Applications of D-dimer Testing
- D-dimer testing can be used to diagnose and manage a vast array of thrombosis-related clinical conditions, including VTE, arterial thrombosis, and disseminated intravascular coagulation (DIC) 2.
- D-dimer testing can be used to identify individuals at increased risk of first thrombotic event, recurrent VTE, and to establish the optimal duration of secondary prophylaxis after a first episode of VTE 2.
- D-dimer testing can be used as a fibrin-related degradation marker for the diagnosis and management of patients with DIC 2.