title: D-dimer concentration increases with age reducing the clinical value of the D-dimer assay in the elderly.
abstract: BACKGROUND
  The D-dimer assay is used as an exclusion test in the assessment of suspected venous thromboembolic disease; patients with a negative result have a low probability of thrombosis. We reviewed the D-dimer results from a hospital and community laboratory using the vidas D-dimer test to assess the influence of age on the D-dimer assay.
  
  
  METHODS
  D-dimer results from 6631 unselected patients aged more than 16 years were analysed in four age groups and it was shown that the median D-dimer concentration increased with age (16-40 years, 294 ng/mL; 40-60 years, 387 ng/mL; 60-80 years; 854 ng/mL; >80 years, 1397 ng/mL). To test the effect of age on the assay specificity, a cohort of 1897 patients with suspected venous thromboembolic disease was analysed separately. Patients with a negative D-dimer were discharged without further investigation. Patients with a positive result and a clinical suspicion of thrombosis underwent further investigation. One hundred and sixty-five deep vein thrombosis or pulmonary embolus cases were identified.
  
  
  RESULTS
  The assay specificity decreased with age from 70% in patients less than 40 years to below 5% in patients more than 80 years. Receiver operator curves were prepared for each age group and the effect of altering the threshold value was analysed. In patients 60-80 years old a threshold value of 1000 ng/mL increased assay specificity to 55% without loss of assay sensitivity.
  
  
  CONCLUSIONS
  The vidas D-dimer assay with a threshold value of 500 ng/mL has little clinical value as an exclusion test in patients more than 80 years old. The assay specificity is poor (26%) in patients aged 60-80 years but could be improved by increasing the threshold value to 1000 ng/mL. We believe that this should be tested in a prospective trial.
authors.affiliation: Department of Haematology, Palmerston North Hospital, Palmerston North, New Zealand. paul.harper@midcentral.co.nz
authors.forename: P L
authors.initials: PL
authors.lastname: Harper
authors.forename: E
authors.initials: E
authors.lastname: Theakston
authors.forename: J
authors.initials: J
authors.lastname: Ahmed
authors.forename: P
authors.initials: P
authors.lastname: Ockelford
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000375:Aging / Q000097:blood*; D015415:Biomarkers / Q000097:blood; D019963:Clinical Chemistry Tests / Q000592:standards; D015331:Cohort Studies; D019281:Dimerization; D005260:Female; D005338:Fibrin Fibrinogen Degradation Products / Q000378:metabolism*; D006801:Humans; D007755:Laboratories, Hospital / Q000592:standards; D008297:Male; D008875:Middle Aged; D012189:Retrospective Studies; D012680:Sensitivity and Specificity; D013923:Thromboembolism / Q000097:blood / Q000175:diagnosis; D020246:Venous Thrombosis / Q000097:blood / Q000175:diagnosis
chemical_list: D015415:Biomarkers; D005338:Fibrin Fibrinogen Degradation Products; C036309:fibrin fragment D