D-Dimer focused testing for PE

The PE testing pathway used, consisted of D-dimer testing. If the D-dimer level was > 500 ng/ mL, a CTPA or VQ scan was performed. If the D-dimer level was less than 500 ng/mL, PE was excluded. Clinicians were permitted to make alternative diagnoses and not perform imaging, even if the d-dimer was high.

Primary Outcome: This included adherence to the D-dimer only testing pathway and the proportion of patients tested for PE who underwent imaging.

Secondary Outcomes:

• PE prevalence among all patients.
• The proportion of PE scans that were positive
• The proportion of imaging ordered without D-dimer or with a negative D-dimer.
• The proportion of imaging not ordered when the D-dimer was positive.
• Length of stay in the ED.
• Time between physician assessment and leaving the ED. 

The primary safety outcome was patients who tested negative for PE, who then had a PE diagnosed in the next 30 days.

N = 10,354

What Did They Find?

10,354 patients were tested for PE

• 3,852 had imaging
• PE was diagnosed in 494 (4.8%) of patients tested.

Primary Outcomes

• There was significantly increased adherence to the pathway in the intervention sites and as would be expected an increase in the numbers of patients who had D-dimer testing ie., from 6.5% to 10.6%.
• Although the proportion of patients tested for PE who underwent imaging was decreased, there was no association with the D-dimer testing only pathway.
• Of the 5,153 patients who tested negative for PE on D-dimer testing, only 2 (0.04%) tested positive for PE in the next 30 days. In comparison, at the control site 3 of 2,886 (0.1%) who tested negative were found to have a PE in the next 30 days.

Secondary Outcomes

• There was a significant association between introduction of the D-dimer-only PE testing pathway and increased diagnoses of PE in the overall population. 
• There was an increased positive yield of pulmonary imaging (aOR 4.89; 95% CI 1.17 to 20.53) at the intervention site.
• There was a significant reduction in patients having PE imaging following a negative D-dimer result.
• There was no effect on the length of stay in the ED, or the length of stay after being assessed by a physician.

• At the control site, there was a significant reduction in the length of stay in the ED.

The authors' conclusion was:

"In this Canadian ED study, the uptake of a D-dimer- only PE testing strategy was sustained and high among emergency physicians. Implementation was associated with higher imaging yield, and a D-dimer result of <500 ng/mL safely excluded PE."

My Take on This

This study tells me a few things:

• D-dimer testing alone is safe, with only a 0.04% miss rate.
• In 96 cases in the study, there was deviation from the protocol, where imaging was performed without D-dimer testing. We are unsure how D-dimer would have performed. Our assumption is that these were considered to be high risk cases and the prevalence of PE in these patients was nearly 22% higher than those of the general study population.
• There may be confounding involved as this is a before-after comparison.
• There were some differences between the intervention and control sites in terms of patient age.
• There needs to be external validation, especially as the rates of PE were low in this study.

Will This study change my practice?

Here are some questions I ask:

• Will I perform a D-dimer if I have a high pre-test probability for a PE and then not image if that's normal. Probably not.
• Will I age adjust? Yes.
• Did this study result in less imaging? Not really.

It won't affect my practice, but it will make me feel better about using the YEARS Study results and knowing that the miss rate with a normal D-dimer is low.

References

1. Germini F et al. Implementation, Clinical Benefit and Safety of a D-Dimer-Focused Pulmonary Embolism testing Pathway in the Emergency Department. Ann Emerg Med. 2024 Apr 23:S0196-0644(24)00156-2. doi: 10.1016/j.annemergmed.2024.03.010. Epub ahead of print. PMID: 38661619.