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P270 Identifying the optimal D-dimer cut off value for ruling out PEs in an ambulatory care setting
  1. FA Khan,
  2. K Ryanna,
  3. E Bailie,
  4. Y Vali
  1. Glenfield Hospital, Leicester, UK

Abstract

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 that using a higher cut off value of D-dimer may improve specificity without affecting sensitivity for a PE.

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.

Receiver operating characteristics (ROC) curve analysis was performed separately for patients with low and intermediate probability, and the optimum cut-off value to exclude PE determined.

Results Of the 2139 patients, prevalence of PE was 3.2% (50/1535) in the low, 14.2% (63/443) in the intermediate and 26% (42/161) in the high probability group. 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.

ROC curve analysis showed the optimum D-dimer cut off value in low risk patients was 0.52, and 0.57 in patients with an intermediate risk.

Abstract P270 Table 1

 

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. A higher D-dimer of 1.0 ug/mL would have correctly avoided 161 scans and subsequently saved over £19,000.2 This must be offset however against patients being incorrectly diagnosed and often ending up in hospital with complications. Using the same cut off of 1.0 ug/mL would have missed a total of 22 PE’s during the study period. Based on this the conventional D-dimer cut off value of 0.5 ug/mL is most appropriate for patients attending the ambulatory PE clinic.

References 1 Venous Thromboembolic diseases: the management of venous thromboembolic diseases and the role of thrombophilia testing. Costing report. NICE, June 2012

2 British Thoracic Society guidelines for the management of suspected acute pulmonary embolism. Thorax 2003;58:470-484

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