D-Dimer Thresholds Rule Out PE in Meta-Analysis

Heidi Splete

December 14, 2021

Adapted D-dimer thresholds based on pretest probability were effective for ruling out pulmonary embolism (PE) in subgroups of high-risk individuals without the use of imaging in a review of data.

In a patient suspected to have a PE, "diagnosis is made radiographically, usually with CT pulmonary angiogram, or V/Q scan," Suman Pal, MD, of the University of New Mexico, Albuquerque, said in an interview.

"Validated clinical decision tools such as Wells' score or Geneva score may be used to identify patients at low pretest probability of PE who may initially get a D-dimer level check, followed by imaging only if D-dimer level is elevated," explained Pal, who was not involved with the new research, which was published in the Annals of Internal Medicine.

According to the authors of the new paper, while current diagnostic strategies in patients with suspected PE include use of a validated clinical decision rule (CDR) and D-dimer testing to rule out PE without imaging tests, the effectiveness of D-dimer tests in older patients, inpatients, cancer patients, and other high-risk groups has not been well-studied.

Lead author of the paper, Milou A.M. Stals, MD, and colleagues said their goal was to evaluate the safety and efficiency of the Wells rule and revised Geneva score in combination with D-dimer tests, and also the YEARS algorithm for D-dimer thresholds, in their paper.

Stals, of Leiden (the Netherlands) University Medical Center, and the coinvestigators conducted an international systemic review and individual patient data meta-analysis that included 16 studies and 20,553 patients, with all studies having been published between Jan. 1, 1995, and Jan. 1, 2021. Their primary outcomes were the safety and efficiency of each of these three strategies.

In the review, the researchers defined safety as the 3-month incidence of venous thromboembolism after PE was ruled out without imaging at baseline. They defined efficiency as the proportion patients for whom PE was ruled out based on D-dimer thresholds without imaging.

Overall, efficiency was highest in the subset of patients aged younger than 40 years, ranging from 47% to 68% in this group. Efficiency was lowest in patients aged 80 years and older (6.0%-23%), and in patients with cancer (9.6%-26%).

The efficiency was higher when D-dimer thresholds based on pretest probability were used, compared with when fixed or age-adjusted D-dimer thresholds were used.

The key finding was the significant variability in performance of the diagnostic strategies, the researchers said.

"The predicted failure rate was generally highest for strategies incorporating adapted D-dimer thresholds. However, at the same time, predicted overall efficiency was substantially higher with these strategies versus strategies with a fixed D-dimer threshold as well," they said. Given that the benefits of each of the three diagnostic strategies depends on their correct application, the researchers recommended that an individual hospitalist choose one strategy for their institution.

"Whether clinicians should rely on the Wells rule, the YEARS algorithm, or the revised Geneva score becomes a matter of local preference and experience," Stals and colleagues wrote.

The study findings were limited by several factors including between-study differences in scoring predictors and D-dimer assays. Another limitation was that differential verification biases for classifying fatal events and PE may have contributed to overestimation of failure rates of the adapted D-dimer thresholds.

Strengths of the study included its large sample size and original data on pretest probability, and that data support the use of any of the three strategies for ruling out PE in the identified subgroups without the need for imaging tests, the authors wrote.

"Pending the results of ongoing diagnostic randomized trials, physicians and guideline committees should balance the interlink between safety and efficiency of available diagnostic strategies," they concluded.

Adapted D-Dimer Benefits Some Patients

"Clearly, increasing the D-dimer cutoff will lower the number of patients who require radiographic imaging (improved specificity), but this comes with a risk for missing PE (lower sensitivity). Is this risk worth taking?" Daniel J. Brotman, MD, of Johns Hopkins University, Baltimore, asked in an editorial accompanying the new study.

Brotman was not surprised by the study findings.

"Conditions that predispose to thrombosis through activated hemostasis – such as advanced age, cancer, inflammation, prolonged hospitalization, and trauma – drive D-dimer levels higher independent of the presence or absence of radiographically apparent thrombosis," he said. However, these patients are unlikely to have normal D-dimer levels regardless of the cutoff used.

Adapted D-dimer cutoffs may benefit some patients, including those with contraindications or limited access to imaging, said Brotman. D-dimer may be used for risk stratification regardless of PE, since patients with marginally elevated D-dimers have better prognoses than those with higher D-dimer elevations, even if a small PE is missed.

Brotman wrote that increasing D-dimer cutoffs for high-risk patients in the subgroups analyzed may spare some patients radiographic testing, but doing so carries an increased risk for diagnostic failure. Overall, "the important work by Stals and colleagues offers reassurance that modifying D-dimer thresholds according to age or pretest probability is safe enough for widespread practice, even in high-risk groups."

Focus on Single Strategy "Based on Local Needs"

"Several validated clinical decision tools, along with age or pretest probability adjusted D-dimer threshold are currently in use as diagnostic strategies for ruling out pulmonary embolism," Pal said in an interview.

The current study is important because of limited data on the performance of these strategies in specific subgroups of patients whose risk of PE may differ from the overall patient population, he noted.

"Different diagnostic strategies for PE have a variable performance in patients with differences of age, active cancer, and history of VTE," said Pal. "However, in this study, no clear preference for one strategy over others could be established for these subgroups, and clinicians should continue to follow institution-specific guidance.

"A single strategy should be adopted at each institution based on local needs and used as the standard of care until further data are available," he said.

"The use of D-dimer to rule out PE, either with fixed threshold or age-adjusted thresholds, can be confounded in clinical settings by other comorbid conditions such as sepsis, recent surgery, and more recently, COVID-19," he said.

"Since the findings of this study do not show a clear benefit of one diagnostic strategy over others in the analyzed subgroups of patients, further prospective head-to-head comparison among the subgroups of interest would be helpful to guide clinical decision making," Pal added.

YEARS-Specific Study Supports D-Dimer Safety and Value

A recent paper published in JAMA supported the results of the meta-analysis. In that study, Yonathan Freund, MD, of Sorbonne Université, Paris, and colleagues focused on the YEARS strategy combined with age-adjusted D-dimer thresholds as a way to rule out PE in PERC-positive ED patients.

The authors of this paper randomized 18 EDs to either a protocol of intervention followed by control, or control followed by intervention. The study population included 726 patients in the intervention group and 688 in the control group.

The intervention strategy to rule out PE consisted of assessing the YEARS criteria and D-dimer testing. PE was ruled out in patients with no YEARS criteria and a D-dimer level below 1,000 ng/mL and in patients with one or more YEARS criteria and D-dimers below an age-adjusted threshold (defined as age times 10 ng/mL in patients aged 50 years and older).

The control strategy consisted of D-dimer testing for all patients with the threshold at age-adjusted levels; D-dimers about these levels prompted chest imaging.

Overall, the risk of a missed VTE at 3 months was noninferior between the groups (0.15% in the intervention group and 0.80% in the controls).

"The intervention was associated with a statistically significant reduction in chest imaging use," the researchers wrote.

This study's findings were limited by randomization at the center level, rather than the patient level, and the use of imaging on some patients despite negative D-dimer tests, the researchers wrote. However, their findings support those of previous studies and especially support the safety of the intervention, in an emergency medicine setting, as no PEs occurred in patients with a YEARS score of zero who underwent the intervention.

Downsides to Applying Algorithms to Every Patient Explained

In an editorial accompanying the JAMA study, Marcel Levi, MD, and Nick van Es, MD, of Amsterdam University Medical Center, emphasized the challenges of diagnosing PE given that many patients present with nonspecific clinical manifestations and without typical signs and symptoms. High-resolution CT pulmonary angiography allows for a fast and easy diagnosis in an emergency setting. However, efforts are ongoing to develop alternative strategies that avoid unnecessary scanning for potential PE patients, many of whom have alternative diagnoses such as pulmonary infections, cardiac conditions, pleural disease, or musculoskeletal problems.

On review of the JAMA study using the YEARS rule with adjusted D-dimer thresholds, the editorialists noted that the data were robust and indicated a 10% reduction in chest imaging. They also emphasized the potential to overwhelm busy clinicians with more algorithms.

"Blindly applying algorithms to every patient may be less appropriate or even undesirable in specific situations in which deviation from the rules on clinical grounds is indicated," but a complex imaging approach may be time consuming and challenging in the acute setting, and a simple algorithm may be safe and efficient in many cases, they wrote. "From a patient perspective, a negative diagnostic algorithm for pulmonary embolism does not diminish the physician's obligation to consider other diagnoses that explain the symptoms, for which chest CT scans may still be needed and helpful."

The Annals of Internal Medicine study was supported by the Dutch Research Council. The JAMA study was supported by the French Health Ministry. Stals, Freund, Pal, Levi, and van Es had no financial conflicts to disclose.

This article originally appeared on MDedge.com, part of the Medscape Professional Network.


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