From the Guidelines
Age adjustment of D-dimer is recommended for patients over 50 years old, using the formula Age × 10 ng/mL, to improve the specificity of the test when ruling out Deep Vein Thrombosis (DVT) or Pulmonary Embolism (PE). This approach is supported by recent studies, including a meta-analysis of 13 studies and 12,497 patients without high pretest probability, which found that the use of age-adjusted D-dimer cutoffs maintained a sensitivity for PE above 97% while significantly increasing specificity 1. The standard D-dimer cutoff of 500 ng/mL often leads to false positives in older patients because D-dimer levels naturally increase with age.
Key Points to Consider
- The age-adjusted formula multiplies the patient's age by 10 to determine the appropriate cutoff value (Age × 10 ng/mL).
- For example, a 70-year-old patient would have an age-adjusted D-dimer cutoff of 700 ng/mL.
- This adjustment maintains the high sensitivity of D-dimer testing while reducing unnecessary imaging studies in older patients.
- Age adjustment should only be applied in outpatients with low or intermediate clinical probability of VTE, not in high-risk patients or those with other conditions that may elevate D-dimer levels such as pregnancy, recent surgery, active cancer, or infection.
Clinical Application
- In patients believed to be at low risk for PE or DVT, the age-adjusted D-dimer cutoff can be used to rule out the condition.
- A normal plasma D-dimer level, using the age-adjusted cutoff, provides sufficient negative predictive value for PE or DVT; no imaging studies are indicated.
- An elevated plasma D-dimer level should lead to imaging studies to confirm the diagnosis.
From the Research
Age Adjustment for D-dimer
The age adjustment for D-dimer in Deep Vein Thrombosis (DVT) screening tests is a crucial aspect of improving the diagnostic specificity for venous thromboembolism, especially in older patients.
- The age-adjusted D-dimer cut-off is calculated as the patient's age multiplied by 10 ng/mL for patients over 50 years old 2, 3, 4, 5, 6.
- This approach has been shown to increase the specificity of D-dimer testing without compromising sensitivity, particularly in patients aged 70 years and older 3, 4, 5, 6.
- Studies have demonstrated that using an age-adjusted D-dimer cut-off can safely exclude DVT in a larger proportion of older patients, reducing the need for unnecessary imaging and associated healthcare costs 2, 3, 4, 5.
Comparison of Age-Adjusted and Conventional Cut-Offs
- The conventional D-dimer cut-off of 500 ng/mL has been compared to age-adjusted cut-offs in several studies, with results showing improved specificity and reduced false positive rates with the age-adjusted approach 2, 3, 4, 5, 6.
- A study published in the Journal of Emergency Medicine found that an age-adjusted cut-off increased specificity from 35.6% to 66.3% while maintaining high sensitivity 2.
- Another study published in the Journal of Thrombosis and Haemostasis found that age-adjusted cut-offs resulted in a significant reduction in false positive results, particularly in patients aged 70 years and older 3.
Clinical Implications
- The use of age-adjusted D-dimer cut-offs has the potential to improve the management of DVT in older patients, both clinically and economically 2, 3, 4, 5, 6.
- By reducing the number of false positive results and unnecessary imaging, age-adjusted cut-offs can help to streamline the diagnostic process and reduce healthcare costs 2, 3.