Introduction Patients attending the ambulatory pulmonary embolism (PE) clinic at the Glenfield Hospital are risk stratified into low, intermediate and high risk based on the BTS scoring.¹ Those with a low or intermediate pre-test probability go on to have a microlatex D-dimer assay and if this is greater than 0.5 ug/mL, imaging in the form of CTPA or VQ scan is carried out.

It has been suggested recently that using age adjusted D-dimers (patient’s age X 10) ug/L in patients above the age of fifty may improve the negative predictive value in ruling out a PE, whilst not affecting sensitivity.²

Methods Data was collected for 2139 consecutive patients who presented to the ambulatory PE clinic between June 2010 and Dec 2014. For each of these patients, age, BTS clinical probability, D-dimer results and final diagnosis was recorded.

For each patient above the age of 50, an age adjusted D-dimer was calculated by multiplying the age by 10. The patient’s actual D-dimer was then compared against the age adjusted D-dimer to determine how many scans could have been avoided, and how many PE’s may have been missed.

Results Above and including the age of 50, there were 660 patients in the low risk, 242 patients in the intermediate risk and 104 in the high-risk categories. Using an age adjusted D-dimer approach would have resulted in 123 scans being rightfully avoided (84 in the low risk and 39 in the intermediate risk), but 6 PE’s would have been missed (2 in the low risk and 4 in the intermediate risk).

No patients with a D-dimer of <0.5 ug/mL who were discharged without any radiological investigations have returned with a missed diagnosis of PE.

Conclusion The optimum D-dimer value must be chosen in the context of missed PEs versus scanning fewer people and thus avoiding unnecessary radiation and using resources more efficiently. An age-adjusted D-dimer in patients above the age of 50 would result in PEs being missed, and a conventional cut off value of 0.5 ug/mL is most appropriate for patients in an ambulatory care setting.

References 1 British Thoracic Society Standards of Care Committee Pulmonary Embolism Guideline Development Group. British Thoracic Society guidelines for the management of suspected acute pulmonary embolism. Thorax 2003;58:470–484

2 Douma RA, le Gal G, Sohne M, 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 2010;340:c1475