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Clinician Article

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Diagnosis of Pulmonary Embolism with d-Dimer Adjusted to Clinical Probability.

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• Kearon C
• de Wit K
• Parpia S
• Schulman S
• Afilalo M
• Hirsch A, et al.

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Clinical Comments

Emergency Medicine

A must-read for emergency medicine. PE is the poster child for emergency medicine over-testing and consequential downstream over-diagnosis and over-treatment (see https://onlinelibrary.wiley.com/doi/full/10.1111/acem.12820). Whereas useful diagnostic tests generally adjust pre-test probabilities for disease, this study uses an innovative approach to adjust "abnormal" for D-dimer based on pre-test probability for VTE. One challenge to widespread uptake of these results to align post-D-dimer imaging decisions with clinical practice is that physicians too often neglect evidence-based risk stratification in advanced imaging (see http://pmid.us/27689922). How would the authors overcome this knowledge translation barrier?

Emergency Medicine

In my opinion, this study is practice-changing. When combined with the previously published YEARS studies, this validates a strategy of doubling the D-Dimer threshold to rule out PE in low-risk patients. The low-risk definition of Wells score =4 allows for most patients to fall into this category (87% in this study) and potentially benefit from the increased likelihood of having PE ruled out without requiring chest imaging. About 1 in 6 patients were able to forego chest imaging who would have required it without the D-Dimer adjustment, and there were no identified misses. I am using this strategy now and encouraging my partners to do the same.

Hemostasis and Thrombosis

Important for all those who diagnose pulmonary embolism from the prestigious Canadian thrombosis research group. These data expand the class of patients for whom diagnostic imaging is not necessary - those with low clinical suspicion and a d-dimer below 1,000 ng/mL, and for moderate-risk patients with d-dimer below 500. Previously, it was considered safe to withhold imaging for low-risk patients with d-dimer below 500, but it was uncertain what to do with moderate risk patients. These new data will change clinical practice BUT with some provisos: 1. The clinician should perform a valid clinical risk score (e.g., Wells) - clinicians don't always do this but rely on gestalt; 2. The conclusions apply to outpatients - Do they mean in an office setting or emergency room? The authors do not specify and the latter could be sicker; 3. These data may not apply to inpatients.

Hemostasis and Thrombosis

An important advance using adjustment of d-dimer values to further curtail unnecessary imaging.

Hospital Doctor/Hospitalists

As a hospitalist, the D-dimer test when <500 ng/ml, is useful to avoid further imaging in a low-risk Wells score. Unfortunately, this combination is not particularly common; whether a slightly higher cutoff (<1000) or lower cutoff with moderate probability would also convey good outcomes was unknown. This study answers that question. Patients with low prob and d-dimer <1000 had excellent 90-day outcomes. 6/1200 were lost to follow-up, which could have affected the final answer slightly. There were too few moderate prob (about 40) to answer that question effectively. However the strategy reduced the need for CTPA by 17%, a very important finding that can stem the tide of over-imaging if applied by all...and it should be.

Internal Medicine

Useful info on decreasing imaging by expanding the definitions of low-prob clinical and negative D-dimer. There were only 40 participants in the moderate-prob group with a negative D-dimer, so the confidence interval here is quite wide and perhaps is not as reassuring. I would also be interested to know how many patients got off-protocol imaging due to clinician preference and what percentage of those images were positive (I didn`t see it in the Results).