D-dimer concentration increases with age reducing the clinical value of the D-dimer assay in the elderly.

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. CONCLUSION: 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.

Transfusion transmitted Yersinia enterocolitica infection in New Zealand.

AIMS: To update and summarise cases of transfusion-transmitted Yersinia enterocolitica infection in New Zealand and to evaluate critically suggested methods to reduce this rare but frequently fatal complication of blood transfusion. METHODS: Case reports of four recent transfusion-transmitted Y. enterocolitica infections in New Zealand are given and previous reports reviewed. Literature review and evaluation of proposed methods to decrease the incidence of transfusing yersinia contaminated blood. RESULTS: There have been eight cases of transfusion-transmitted Y. enterocolitica infection in New Zealand in the past five years. Four of the five deaths have been directly caused by the transfusion. This gives a transfusion incidence rate of one:65,000 and a fatality rate of one:104,000 units transfused. This fatality rate is more than 80 times higher than that reported in the United States. CONCLUSIONS: Why the incidence of transfusion-transmitted yersinia is so high is not clear, since we do not store blood as long as many other countries, particularly the United States. In Auckland, however, the cases came at a time when the number of yersinia isolates from the community is reported to be rising. Many suggestions for the prevention of this problem have been put forward reflecting the fact that there is as yet no perfect solution. Those which are easy to implement and cheap to perform are largely already in place and investigation is continuing into the other alternatives.

Autologous blood transfusion in Auckland.

AIMS: To review autologous blood collection and transfusion practice in Auckland over the last five years. METHOD: Records of autologous blood collections were obtained from blood collection centre records and results of transfusions on patients from hospital notes. RESULTS: One hundred and sixty-four units of blood were collected from 77 patients. Seventy-five percent of the units collected were transfused. Most autologous blood was transfused to private hospital patients. Only 8% of patients required homologous blood. CONCLUSIONS: There has been a slow increase of autologous blood collection and transfusion in the Auckland area, as well as in the rest of New Zealand. The present risks of homologous transfusion, particularly since the introduction of hepatitis C testing, appear very low. A further expansion of the present autologous blood programme would entail increased expenditure and it is suggested that a critical cost benefit analysis would be useful before the programme is expanded.