From the Guidelines
**A D-dimer result of <0.22 mg/L FEU is considered normal and effectively rules out conditions like deep vein thrombosis (DVT), pulmonary embolism (PE), or disseminated intravascular coagulation (DIC) in patients with low to moderate clinical suspicion**. This is based on the high negative predictive value of D-dimer testing, as reported in the 2020 European Society of Cardiology (ESC) guidelines for the diagnosis and management of acute pulmonary embolism 1. The guidelines state that a normal D-dimer level renders acute PE or DVT unlikely, and the number of patients in whom D-dimer must be measured to exclude one PE rises from 3 in the general population of an emergency department to >10 in specific situations such as cancer, hospitalized patients, or pregnancy.
Some key points to consider when interpreting D-dimer results include:
- D-dimer has high sensitivity but low specificity, making it useful for ruling out conditions but not confirming them 1
- False negatives can occasionally occur, particularly in small clots, chronic thromboembolic disease, or if testing is performed too early after symptom onset
- Clinical assessment remains important, as D-dimer results should be considered in the context of the patient's overall clinical presentation
- Additional imaging studies like ultrasound or CT angiography may still be warranted if clinical suspicion remains high despite a negative D-dimer result
The 2014 ESC guidelines also support the use of D-dimer testing for ruling out PE, with a meta-analysis showing that the three-month thromboembolic risk was <1% in patients left untreated on the basis of a negative test result 1. However, the 2020 guidelines provide more up-to-date and comprehensive guidance on the use of D-dimer testing in the diagnosis and management of acute pulmonary embolism.
In terms of the diagnostic yield of D-dimer, it relies on its specificity, which varies according to patient characteristics, such as age and comorbidities 1. The specificity of D-dimer in suspected PE decreases steadily with age and may reach 10% in patients above 80 years. Therefore, the number of patients with suspected PE in whom D-dimer must be measured to exclude one PE varies between 3 in the emergency department and 10 or above in specific situations. Deciding whether measuring D-dimer is worthwhile in a given situation remains a matter of clinical judgement.
From the Research
D-Dimer Test Results
- The D-Dimer test result is <0.22 mg/L FEU, which is below the threshold for diagnosing venous thromboembolism (VTE) 2, 3, 4, 5, 6.
- A low D-Dimer level can help exclude VTE, including deep vein thrombosis (DVT) and pulmonary embolism (PE), in patients with low to intermediate pretest probability 3, 5, 6.
Diagnostic Pathway
- The diagnostic pathway for VTE involves assessing pretest clinical probability and using evidence-based algorithms 2, 3, 5.
- D-Dimer tests can reduce the need for subsequent diagnostic procedures, such as imaging tests 2, 3, 4, 5, 6.
- If the pretest probability is high or the D-Dimer level is above the threshold, imaging tests, such as compression ultrasound or chest CT, are recommended 3, 5, 6.
Clinical Management
- Clinical management of PE is guided by risk stratification according to early mortality 2.
- Anticoagulation therapy is the foundation of treatment for VTE, and patients should receive anticoagulation maintenance therapy for 3-6 months 2, 3, 5.
- The duration of subsequent secondary prophylaxis depends on the presumed risk of VTE recurrence and bleeding 2, 5.
D-Dimer Testing
- D-Dimer testing has high sensitivity but low specificity, and levels can be elevated in conditions other than thrombosis 4, 6.
- D-Dimer levels can be affected by patient characteristics, such as age, pregnancy, renal function, or cancer 6.
- Adjusting D-Dimer cutoffs according to patient characteristics may improve diagnostic accuracy 6.