What if the EHR Age-Adjusts D-dimer for You?

Written by Bo Stubblefield

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Using an EHR-based tool to age-adjust D-dimers resulted in less imaging for patients being evaluated for acute pulmonary embolism (PE).

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Why does this matter?
Reducing imaging in low and intermediate risk patients with suspected PE is the name of the game. This reduction in imaging not only reduces exposure to ionizing radiation and contrast to the patient, but also reduces length of stay and overall cost (1). As demonstrated in the ADJUST-PE trial, using a patient’s age (if age> 50, threshold = age x 10)* to adjust the D-dimer threshold is a well validated, safe approach that allows more patients to be ruled out without imaging (2). This is a Level B recommendation from ACEP (3). The D-dimer is a highly sensitive test, but has a low specificity, which makes it useful in ruling out PE in low and intermediate risk groups. The specificity of the D-dimer decreases with age, thus age-adjusting cutoffs may increase the specificity of D-dimer and reduce unnecessary diagnostic imaging (4). What happens if we let the EHR adjust it for us?

Let the EHR do the work…
This was a retrospective, pre/post implementation study conducted in a U.S. healthcare system comprising six hospitals. The pre-implementation cohort used the positive reference value D-dimer cutoff of 0.5 ug/mL. In the post-implementation cohort, the EHR displayed an adjusted D-dimer cutoff using the formula: Age (years) x 0.01 ug/mL (i.e. a 67-year-old patient now has a positivity threshold of 0.67 ug/mL). The D-dimer assay used in each of the 6 hospitals was the STA Liatest® D-Di manufactured by Diagnostica Stago. Of note, an EHR decision support tool encouraging providers to risk stratify patients using PERC, Wells, or Geneva was already in place in each of the hospital systems. The primary outcome was the proportion of patients who underwent imaging either by CTPA or V/Q scan.

As expected, a lower proportion of patients had a positive D-dimer following implementation of the age-adjusted cutoff. This resulted in an absolute risk reduction of 4.4% or 1,104 fewer CT scans in the post-implementation group. D-dimer test validity post-intervention demonstrated an unchanged sensitivity with an increased specificity (52.6% pre v. 58.2% post, p<0.05) and increased diagnostic accuracy (53.7% pre v. 59.2% post, p<0.05).

*Another Spoonful on D-dimer interpretation – units & concentrations reported
D-dimer interpretation can get tricky. You are not alone if this confuses you. ADJUST-PE compared the age-adjusted cutoff with a fixed cutoff of 500 µg/L. This study used a fixed cutoff of 0.5 µg/mL for comparison. Your institution will vary in the units and concentrations reported for your D-dimer depending on the assay used. Let MDCalc to do the heavy lifting and simply select the units reported: DDU or FEU and concentration:µg/mL or µg/L (µg/L is mathematically equivalent to ng/mL).

Multi-center implementation of automated age-adjusted D-dimer results reduces unnecessary PE imaging. Am J Emerg Med. 2021 Feb;40:181-183. doi: 10.1016/j.ajem.2020.10.067.

Reviewed by Clay Smith

Works Cited

  1. De Pooter N, Brionne-François M, Smahi M, Abecassis L, Toulon P. Age-adjusted D-dimer cut-off levels to rule out venous thromboembolism in patients with non-high pre-test probability: Clinical performance and cost-effectiveness analysis. Journal of thrombosis and haemostasis : JTH 2021.

  2. Righini M, Van Es J, Den Exter PL, et al. Age-adjusted D-dimer cutoff levels to rule out pulmonary embolism: the ADJUST-PE study. Jama 2014;311:1117-24.

  3. American College of Emergency Physicians Clinical Policies Subcommittee on Thromboembolic D, Wolf SJ, Hahn SA, et al. Clinical Policy: Critical Issues in the Evaluation and Management of Adult Patients Presenting to the Emergency Department With Suspected Acute Venous Thromboembolic Disease. Annals of emergency medicine 2018;71:e59-e109.

  4. Crawford F, Andras A, Welch K, Sheares K, Keeling D, Chappell FM. D-dimer test for excluding the diagnosis of pulmonary embolism. Cochrane Database Syst Rev 2016:CD010864.

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