When to Order a D-Dimer Test
Order a D-dimer test in patients with low or intermediate pretest probability of pulmonary embolism (PE), or in low-risk patients who do not meet all Pulmonary Embolism Rule-Out Criteria (PERC). Do not order D-dimer in high-risk patients—proceed directly to imaging. 1
Risk Stratification First: The Essential First Step
Before ordering any D-dimer test, you must stratify the patient's pretest probability using validated clinical prediction rules such as the Wells score or revised Geneva score. 1, 2 This step is non-negotiable and determines your entire diagnostic pathway.
When D-Dimer Testing is Appropriate:
Low pretest probability patients who do NOT meet all PERC criteria: These patients require D-dimer testing to further risk-stratify. 1
Intermediate pretest probability patients: D-dimer serves as the initial diagnostic test before considering imaging. 1, 2
Outpatients and emergency department patients: D-dimer is most validated in these settings to reduce unnecessary imaging and radiation exposure. 2
When D-Dimer Testing Should NOT Be Ordered:
High pretest probability patients: Skip D-dimer entirely and proceed directly to CT pulmonary angiography (CTPA), as even a normal D-dimer does not safely exclude PE in this population. 1, 2
Low-risk patients meeting ALL PERC criteria: These patients are at such low risk (<1%) that even D-dimer testing poses more harm than benefit through false-positive results. 1
Age-Adjusted D-Dimer Cutoffs: Critical for Patients Over 50
Use age-adjusted D-dimer thresholds (age × 10 ng/mL) rather than the fixed 500 ng/mL cutoff in patients older than 50 years. 1, 2 This approach dramatically improves diagnostic yield in elderly patients:
In patients ≥75 years old, age-adjusted cutoffs increase the proportion who can avoid imaging from 6.4% to 29.7%, without missing PE cases. 3
The age-adjusted cutoff has been prospectively validated with a failure rate of only 0.3% (1 in 331 patients). 3
This strategy has also been validated for deep vein thrombosis, with 0% failure rate in patients with D-dimer between 500 µg/L and their age-adjusted cutoff. 4
Common Pitfalls to Avoid:
Specificity decreases in inpatients: D-dimer has lower specificity in hospitalized patients compared to outpatients due to comorbidities, but it remains highly sensitive and appropriate for ruling out PE when combined with proper risk stratification. 1
Caution with YEARS algorithm: While the YEARS algorithm allows PE exclusion with D-dimer <1000 ng/mL in patients with zero YEARS criteria, external validation found 6.3% PE prevalence in patients with D-dimer <1000 ng/mL but above their age-adjusted cutoff. 5 Consider using age-adjusted cutoffs even within the YEARS framework.
Use highly sensitive assays: Only highly sensitive D-dimer assays (enzyme-linked immunosorbent assays) can safely rule out PE in both low and intermediate-risk patients; older latex or erythrocyte agglutination assays are only reliable for low-risk patients. 1
The Complete Diagnostic Algorithm:
Assess pretest probability using Wells score or revised Geneva score 1, 2
If high probability: Order CTPA immediately; do not order D-dimer 1, 2
If low probability AND meets all PERC criteria: No testing needed 1
If low probability but does NOT meet all PERC criteria OR intermediate probability: Order highly sensitive D-dimer with age-adjusted cutoff (age × 10 ng/mL for patients >50 years) 1, 2
If D-dimer below age-adjusted cutoff: PE excluded; no imaging needed 1, 2