Age adjusted D-dimer

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Background

  • The PE derivation and validation study for usage of the age adjusted d-dimer formula concluded that when combining the d-dimer adjustment with clinical probability, less patients required CTA for exclusion and offered no clinical increase in the rate of missed Pulmonary embolism[1][2]
  • Similarly, using the age adjusted d-dimer in combination with clinical probability can reduce the need for further testing in DVT evaluations with no substantial risk to patient safety[3][4][5]

Usage

Labs commonly report the test as fibrinogen equivalent units (FEUs) with the cutoff at 500 ng/mL and most studies used the FEU values for derivation or validation. If reported by the lab as a D-dimer unit (DDU) the cutoff is often 230 ng/mL. 2 FEUs equal 1 DDU.

  • Age (years) x 10 ug/L for patients > 50 years of age
    • Patient age 75 = age adjusted d-dimer of 750 ug/L
  • If using a lab with a cutoff of 230 (DDU assay) then formula is Age x 5
TEST Age Sensitivity Specificity
Lab cutoff 51 - 60 100% 57.60%
Lab cutoff 61 - 70 99.00% 39.40%
Lab cuttoff 71 - 80 98.70% 24.50%
Lab cutoff >80 99.60% 14.70%
Age Adjusted cutoff 51 - 60 99.40% 62.30%
Age Adjusted cutoff 61 - 70 97.30% 49.50%
Age Adjusted cutoff 71 - 80 97.30% 44.20%
Age Adjusted cutoff >80 97.00% 35.20%

Special Considerations

  • Risk stratification for all patients should take place using the Wells Criteria
  • Know your lab's assay cutoff and whether it is report as DDU or FEUs since the formula is different for the different assays

See Also

References

  1. Douma R. et al. Potential of an age adjusted D-dimer cut-off value to improve the exclusion of pulmonary embolism in older patients: a retrospective analysis of three large cohorts. BMJ (Clinical research ed.) (March 30). 2010. doi:10.1136/bmj.c1475.
  2. Douma, R. et al. Using an age-dependent D-dimer cut-off value increases the number of older patients in whom deep vein thrombosis can be safely excluded. Haematologica, no. 10 (April 17). 2012. doi:10.3324/haematol.2011.060657.
  3. Schouten, H et al.. Diagnostic accuracy of conventional or age adjusted D-dimer cut-off values in older patients with suspected venous thromboembolism: systematic review and meta-analysis. BMJ (Clinical research ed.) (May 3). 2013. doi:10.1136/bmj.f2492.
  4. Schouten, H et al. Validation of two age dependent D-dimer cut-off values for exclusion of deep vein thrombosis in suspected elderly patients in primary care: retrospective, cross sectional, diagnostic analysis. BMJ (Clinical research ed.) (June 6). 2012. doi:10.1136/bmj.e2985.
  5. Adams, D, et al. Clinical utility of an age-adjusted D-dimer in the diagnosis of venous thromboembolism. Ann Emerg Med. 2014; 64:232-234.