The Inappropriate Use of the SimpliRed D-Dimer Assay in the Diagnosis of Venous Thromboembolism,
Bibliographic record
Abstract
Abstract 4207 Introduction: Multiple diagnostic tests are available to evaluate patients with suspected venous thromboembolism (VTE). The diagnosis of VTE involves combining a clinical pre-test probability using validated scoring systems such as the Wells score (Wells, 2000) with laboratory testing and/or diagnostic imaging. The D-dimer assay is a highly sensitive screening test for VTE that has been shown to safely exclude VTE in patients with low pre-test probability (Kearon, 2006). This project was aimed at determining if the SimpliRed D-dimer assay is used appropriately at our institution. More specifically, we wanted to determine if it is being used in patients with low clinical probability of pulmonary embolism (PE) or deep vein thrombosis (DVT) based on the Wells score and in the absence of other variables which could falsely elevate the D-dimer as determined by expert opinion. Methods: A retrospective review of 199 charts from St. Joseph's Hospital in Hamilton, Ontario from March 2007 to April 2007 was performed. Information was obtained on a standardized data collection form. Duplicate data extraction of the first 20 charts was undertaken to ensure concordance. Results: Of the 199 SimpliRed D-dimer assays ordered during this time period, 84 (42%) were inappropriate. Forty (48%) were considered inappropriate because they were ordered in patients with a moderate to high pre-test probability for VTE while 44 (52%) were ordered in patients with a co-existing medical condition that should have precluded the use of the assay including sepsis, pregnancy, active malignancy, and recent major surgery. The D-dimer assay was positive in 51 (61%) of the 84 inappropriate tests and 31 of these patients underwent further testing. Twelve patients were eventually diagnosed with VTE. The remaining 20 patients with a positive D-dimer ordered in an inappropriate context did not undergo further testing to investigate the positive result. Thirty-three (41%) patients with an inappropriately ordered D-dimer had a negative result and did not undergo further investigation. For patients with an appropriately ordered D-dimer assay (115 out of 199 or 58%), 96 had a negative D-dimer result. Of the 96, 28 patients went on to further testing including Doppler ultrasounds, ventilation/perfusion scans, or CT scans. One of the 28 patients had VTE. Conclusions: This retrospective review revealed that 42% of the SimpliRed D-dimer assays ordered at our institution are inappropriate. Thirty three patients identified in this review who had a non-low pretest probability and negative D-dimer did not undergo further testing. A negative D-dimer result in these patients is not sufficient to rule out VTE – the lack of further appropriate testing could have led to missed VTE events. D-dimer assays, including the one used at our institution, have been shown to reliably rule out both DVT and PE in patients with a low pre-test probability (Kearon, 2006). At our institution 28 patients with an appropriately ordered, negative D-dimer underwent further testing that would not be recommended based on current diagnostic algorithms. These investigations are costly and expose the patient to possible unnecessary harm (such as radiation exposure from CT scans or use of anticoagulants until testing can be arranged). Of the patients with a negative D-dimer who went on to have further investigations, 1 was found to have VTE. This patient may have had a higher clinical pre-test probability than was assigned retrospectively from limited chart records. If the pre-test score assigned was accurate, this suggests that the failure rate of the D-dimer for ruling out VTE in a patient with a low pre-test probability is 3.6% (0.1% to 18.3%) in our series, higher than previously reported (Kearon, 2006). Disclosures: Crowther: Pfizer: Consultancy, Research Funding; Leo Pharma: Consultancy, Research Funding; Bayer: Consultancy; CSL: Consultancy; BI: Consultancy, Research Funding; Behring: Consultancy; Octapharma: Consultancy; Artisan: Consultancy.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.002 | 0.016 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.000 | 0.001 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".