A Review of Inappropriate D-Dimer Ordering at a Canadian Tertiary Care Centre

Introduction

The D-dimer has been validated for use in the diagnosis of venous thromboembolism (VTE). The high sensitivity of the assay allows for safe exclusion of VTE in patients with low pre-test probability. Pre-test probability scores such as the Wells score for Deep Vein Thrombosis (DVT) and Pulmonary Embolism (PE) have been established to help guide physicians on when to order a D-dimer in patients with suspected VTE.

We sought to explore the landscape of D-dimer ordering at our institution and what clinical circumstances trigger D-dimer ordering.

Methods

We conducted a retrospective chart review of 237 patients in whom a D-dimer has been ordered over a 3-month period from January to March 2018 at the University of Alberta Hospital, Edmonton, Canada. Charts were reviewed for the following parameters: Specialty of ordering physician, apparent indication for ordering, patient risk factors for VTE and evidence of pre-test probability calculation. If no pre-test probability was recorded, we retrospectively calculated Wells DVT or PE scores depending on the apparent indication. We then reviewed subsequent investigations thought to be influenced by interpretation of the D-dimer. These included ventilation/perfusion scans (V/Q scan), ultrasound Doppler studies and Computerized Tomography pulmonary angiography (CTPA).

Results

Of the 237 charts reviewed, 84.4% of D-dimers were ordered in the Emergency Department while only 14.3% were drawn on admitted patients. Sixty-nine percent of the patients were identified as having at least one risk factor for the development of VTE with prolonged hospitalization (5.5%) and personal history of VTE (4.2%) being the most common. Indication for ordering was suspected VTE in 76.3% of patients while the indications was unclear in 12.7% of patients. An initial pre-test probability score was recorded for only 3 patients. Of the D-dimers ordered, 47.7% were above the upper limit of normal (≥ 0.50 mg/L) and considered a positive test. Forty five CTPAs and 27 V/Q scans were performed with only 4 (1.69%) and 6 (2.53%) confirming the presence of pulmonary emboli, respectively. Doppler ultrasounds were performed on 18 patients (7.6%) with only one confirming a DVT.

Conclusions

Our data shows that the majority of physicians at our institution fail to utilize pre-test probability tools prior to ordering a D-dimer. This leads to unnecessary costs, overuse of imaging studies and results in low rates of positive scans.