From the Guidelines
Age significantly affects D-dimer cutoff values, with higher thresholds needed for older patients to maintain clinical utility, and an age-adjusted cutoff formula of Age × 10 ng/mL for patients over 50 years is recommended. The standard D-dimer cutoff of 500 ng/mL works well for younger patients but produces excessive false positives in older individuals due to naturally increasing D-dimer levels with age 1. To address this, using age-adjusted d-dimer cutoffs for patients older than 50 years maintains a sensitivity for PE above 97% while significantly increasing specificity 1. Some key points to consider when using D-dimer tests include:
- The physiological basis for this age-related increase in D-dimer levels includes greater baseline activation of the coagulation system, reduced clearance of fibrin degradation products, and increased prevalence of comorbidities that elevate D-dimer levels in older adults.
- Using age-adjusted cutoffs helps clinicians avoid unnecessary imaging studies while maintaining the test's value as a rule-out tool for thrombotic conditions.
- For patients at low or intermediate pretest probability of PE, a normal plasma d-dimer level, ideally age-adjusted, provides sufficient negative predictive value for PE; no imaging studies are indicated 1.
- An elevated plasma d-dimer level should prompt imaging studies, regardless of the patient's age or pretest probability 1.
From the Research
D-Dimer Test and Age
The D-dimer test is used to diagnose thromboembolic events, but its usefulness decreases in older patients due to a lower specificity. Several studies have investigated the use of age-adjusted D-dimer cut-off values to improve the exclusion of pulmonary embolism and deep vein thrombosis in older patients.
Age-Adjusted D-Dimer Cut-Off Values
- The age-adjusted D-dimer cut-off value is calculated as (patient's age x 10) μg/L in patients over 50 years 2, 3, 4, 5.
- This cut-off value has been validated in several studies and has been shown to increase the proportion of older patients in whom thromboembolic events can be safely excluded 2, 3, 4, 5, 6.
- The use of age-adjusted D-dimer cut-off values has been shown to decrease the false positive rate and increase the negative predictive value of the D-dimer test in older patients 2, 3, 4, 5, 6.
Benefits of Age-Adjusted D-Dimer Cut-Off Values
- The age-adjusted D-dimer cut-off value increases the proportion of patients over 70 years in whom deep vein thrombosis can be excluded by 19% 3.
- The use of age-adjusted D-dimer cut-off values reduces the number of unnecessary imaging tests and decreases the number needed to test (NNT) to rule out pulmonary embolism in older patients 4, 5, 6.
- The age-adjusted D-dimer cut-off value has been shown to have a low negative likelihood ratio (nLR) and can be used as a rule-out strategy for pulmonary embolism in non-high pretest clinical probability patients 4.