A Randomized, Controlled Trial of Varying D-Dimer Cutpoints According to Clinical Pretest Probability Compared with a Uniform D-Dimer Cutpoint for Diagnosis of Deep Vein Thrombosis
Bibliographic record
Abstract
Abstract Abstract 5116 Background: D-dimer assays are currently used as a one-size-fits-all diagnostic test for DVT where the same cutpoint is used to define a positive result for all patients. This approach ignores the relationship between the diagnostic properties of the assay and the pretest probability of the disease. Objective: We conducted a randomized, allocation concealed, controlled, assessor-blinded trial to compare the safety and efficiency of two diagnostic strategies for D-dimer testing for first acute DVT of the lower limb: Selective use of D-dimer testing, using different D-dimer cutpoint levels according to clinical pretest probability (C-PTP) and the traditional Uniform approach. Method: 1723 consecutive eligible inpatients and outpatients at 5 clinical centres (4 in Ontario, 1 in Montreal) had their C-PTP assessed using the Wells' Score and were randomized to either: Uniform D-dimer testing, in which all patients had a D-dimer test and a level of <0.5 μ g fibrinogen equivalent units (FEU)/mL was classified as negative (the control group); or Selective D-dimer testing, in which D-dimer testing was (a) performed in patients with Low and Moderate C-PTP only, (patients with a High C-PTP had an ultrasound, but no D-dimer testing), and (b) was classified as negative if the D-dimer level was <0.5 μ g FEU/mL with Moderate C-PTP or <1.0 μ g FEU/mL with Low C-PTP (the experimental group). The D-dimer assays used in this study were the MDA D-Dimer (bioMerieux, Inc and Trinity Biotech) and STA Liatest D-Dimer(Diagnostica Stago). All patients with a positive D-dimer had an ultrasound of their leg. Symptomatic venous thromboembolic events (VTE) during 3 months of follow-up were objectively confirmed and independently adjudicated. Results: The incidence of VTE during 3 months of follow-up in patients who were not diagnosed with DVT at initial presentation was 1.1% (9/811) with Uniform testing, and 1.1% (9/814) with Selective testing (difference 0.004%, 95% CI:-1.122, 1.111). The incidence of VTE during 3 months of follow-up in patients in the Low C-PTP Select arm (D-dimer cutpoint 1.0 μ g FEU/mL) was 0% (0/356), and in the Low C-PTP Uniform arm (D-dimer cutpoint 0.5 μ g FEU/mL), it was 0.3% (1/336). Conclusion: This is the first randomized controlled clinical trial to show that Selective use of D-dimer testing, with a higher D-dimer cutpoint in patients with Low C-PTP, is safe and potentially more efficient than current practice. Funded by the Heart & Stroke Foundation of Ontario. Disclosures: Linkins: Trinity Biotech: in-kind donation of D-dimer kits; BioMerieux: in-kind donation of D-dimer kits; Stago Diagnostica: in-kind donation of D-dimer kits. Bates:bioMerieux: in-kind donation of D-dimer kits; Trinity Biotech: Consultancy, in-kind donation of D-dimer kits. Kearon:BioMerieux: in-kind donation of D-dimer kits; Trinity Biotech: in-kind donation of D-dimer kits; Stago Diagnostica: in-kind donation of D-dimer kits.
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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 | 0.005 | 0.011 |
| Meta-epidemiology (narrow) | 0.003 | 0.001 |
| Meta-epidemiology (broad) | 0.006 | 0.003 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.001 | 0.003 |
| Scholarly communication | 0.002 | 0.002 |
| Open science | 0.002 | 0.001 |
| Research integrity | 0.004 | 0.004 |
| Insufficient payload (model declined to judge) | 0.010 | 0.001 |
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".