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Xu K, de Wit K, Geersing GJ, et al. A simplified decision rule to rule out deep vein thrombosis using clinical assessment and D-dimer. J Thromb Haemost. 2021 Apr 8. doi: 10.1111/jth.15337. (Original study)

BACKGROUND: Current clinical decision rules to exclude deep vein thrombosis (DVT) are underused partly because of their complexity. A simplified rule that can be easily applied would be more appealing to use in clinical practice.

METHODS: We used individual patient data from prospective diagnostic studies of patients suspected of DVT to develop a new clinical decision rule. The primary outcome was presence of DVT either at initial testing or during follow-up. DVT was considered safely excluded if the upper 95% confidence interval (CI) of DVT prevalence was <2%.

RESULTS: Four studies and 3368 patients were eligible for this analysis. Overall prevalence of DVT was 17%. In addition to D-dimer, two variables, calf swelling and DVT as the most likely diagnosis, are included in the new rule. Based on these two variables, two clinical pretest probability (CPTP) groups were defined; low (none of the two items present) and high (at least one of the items present). DVT can be safely excluded in patients with low CPTP with a D-dimer <500 ng/mL (prevalence = 0.1%; 95% CI, 0.0-0.8), low CPTP with a D-dimer between 500 ng/ml and 1000 ng/ml (prevalence = 0.3%; 95% CI, 0.0-1.7), and D-dimer <500 ng/ml in patients with high CPTP (prevalence = 0.3%; 95% CI, 0.0-1.0).

CONCLUSIONS: The combination of D-dimer and Wells items resulted in a simple clinical decision rule with 3 items. The results suggest that the rule can safely exclude DVT. Prospective validation is required.

Discipline Area Score
Hematology 7 / 7
Hemostasis and Thrombosis 6 / 7
Family Medicine (FM)/General Practice (GP) 6 / 7
Emergency Medicine 6 / 7
General Internal Medicine-Primary Care(US) 6 / 7
Hospital Doctor/Hospitalists 6 / 7
Internal Medicine 6 / 7
Comments from MORE raters

Emergency Medicine rater

Current DVT decision aids are not overly complex or difficult to integrate into diagnostic pathways. In my opinion, more decision aids are not the highest priority. Instead, defining "over-testing" and "over-diagnosis" in a transdisciplinary way should be prioritized (https://onlinelibrary.wiley.com/doi/full/10.1111/acem.12820) and then applying Implementation Science to close Knowledge Translation leaks (https://onlinelibrary.wiley.com/doi/full/10.1111/acem.12828).

Emergency Medicine rater

This study sought to derive and evaluate a new clinical decision rule using a simplified version of Wells combined with D-dimer to evaluate DVT. The authors incorporated individual patient data from 4 studies with 3368 patients and an overall DVT prevalence of 17%. They incorporated two variables: calf swelling > 3 cm and "DVT as the most likely diagnosis" with D-dimer testing. If neither of these factors were present, a D-dimer < 1000 ng/mL could safely exclude DVT. In this subgroup, DVT was present in 0.1% of those with D-dimer < 500 and 0.3% in those with D-dimer 500-999. In those with at least one risk factor, D-dimer < 1000 could safely exclude DVT (prevalence 0.3%). Overall, sensitivity was 98.1%, with an NPV of 99.3%. DVT could be safely excluded in 43% of patients in the data set. This is very promising, but there are limitations. The rule utilizes physician gestalt in DVT assessment and, more importantly, prospective validation is required to evaluate safety and efficacy.

Emergency Medicine rater

Similar to the YEARS algorithm, the DAYS algorithm is a simplified version of Wells and D-dimer. The DAYS algorithm also utilizes 2 cutoffs for D-dimer, similar to YEARS depending on the pre-test probability. What is great in this study is that the pre-test probability is simplified to just 2 questions instead of 9, relying on calf swelling and "DVT is the most likely diagnosis." However, there are some limitations: 1) "DVT is the most likely diagnosis" can sway the value of D-dimer used, the pre-test probability must be calculated prior to utilizing the D-dimer in the algorithm; 2) "DVT is the most likely diagnosis" is the most variable (ambiguous) of the Well`s criteria and would likely require some degree of clinical experience; 3) external validation is needed to see whether the results play out in the real world (as opposed to the 3 studies this is based on).

Family Medicine (FM)/General Practice (GP) rater

This decision tool needs to be prospectively validated before it’s ready for prime time.

Hemostasis and Thrombosis rater

Not sure this is a significant improvement on previously published clinical decision rules for DVT diagnosis because one of the 3 elements requires a very subjective judgment by the clinician.

Hemostasis and Thrombosis rater

Suggests that the full Wells score may not be needed and a simplified score may be as valid when combined with D-dimer testing. Although the authors state that the Wells score may not be used or may be used incorrectly due to complexity, it is relatively easy to use. The advantage of the new score is likely not great.

Hemostasis and Thrombosis rater

As a haematologist, these results are promising for simplifying DVT diagnosis. If prospectively validated, this will likely have practice-changing implications in the Emergency Room and family physician`s office.

Hospital Doctor/Hospitalists rater

Very simple and evidence-based clinical prediction rule.

Internal Medicine rater

Based on retrospective validation of previous study data and requires prospective validation.
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