Age-Adjusted D-dimer for Venous Thromboembolism (VTE)

Age-Adjusted D-dimer Calculator

Age

years

D-dimer

ng/mL

Age-Adjusted Threshold: –

–

Adjusts D-dimer cutoffs to help rule out VTE in patients ≥50 years old.

Why Use

This has been proposed to increase throughput time and decrease unnecessary testing and complications in patients. Accepted by ACEP and ACP as acceptable in risk-stratifying low- to intermediate-risk patients.

When to Use

Patients ≥50 years old presenting to emergency department as outpatients who are being worked up for PE and have low to intermediate pretest probability. Do not use in high-risk patients (i.e., those who would proceed to imaging regardless of D-dimer result).

Formula

Units Age-adjusted D-dimer cutoff FEU (fibrinogen equivalent units) Age × 10 µg/L DDU (D-dimer units) Age × 5 µg/L Example: For a patient aged 68 years, the D-dimer concentration (FEU assay) would be considered normal below 680 μg/L (68 × 10 µg/L), also equivalent to 680 ng/mL or 0.680 µg/mL. Note: should only be used in patients ≥50 years of age. Check your lab result carefully for unit of measure (e.g. μg/L or ng/mL vs µg/mL) and type of unit (FEU vs DDU).

Pearls / Pitfalls

Has been shown to significantly increase specificity in older populations with minimal reduction in sensitivity. Can be used for assays that report fibrinogen equivalent units (FEU) with a D-dimer cutoff of 500 µg/L, or D-dimer units (DDU, less common) with a D-dimer cutoff of 250 µg/L. A value below age × 10 µg/L (5 µg/L for DDU assays) adequately rules out the need for further testing for PE in low- to intermediate-risk patients. Note that there is currently no standard D-dimer unit of measure, and there is wide variation among labs in cutoffs reported and magnitude of unit (e.g. µg/L vs ng/mL vs µg/mL). While traditional teaching previously dictated that D-dimer should only be used in low-risk patients, this was based on lower sensitivity of D-dimer assays at the time. Modern D-dimer assays (immunoturbidimetric) have sensitivities up to 100% ( Knecht 1997 , Righini 2014 ).

Management

A patient with a D-dimer above the age-adjusted cutoff should undergo confirmatory testing with imagi ng ( i.e., C TA, V/Q scan).

Advice

The goals of the age-adjusted D-dimer is to increase the specificity of the test in patients ≥50 years old and prevent unnecessary testing and complications. Use of the age-adjusted D-dimer is not appropriate for patients who are high-risk based on clinical gestalt or clinical prediction scores, such as the Wells’ Score for PE (scores >4) or Revised Geneva Score (scores >11).

More Information

Interpretation: Age-adjusted D-dimer VTE diagnosis Recommendation At or above cutoff Likely Consider confirmatory testing with CTA or V/Q scan Below cutoff Unlikely Consider alternative diagnosis