Age Adjusted D-dimer
For our next installment of Clinical Conundrums, we are going to address the issue of the Age Adjusted D-dimer in our hospital. Can we age adjust the SIUH (230) D-dimer for appropriate patients with suspected PE?Take a read and, perhaps, your practice will be changed!
Can you age adjust the SIUH D-dimer for appropriate patients with suspected PE?
Bottom Line Up Top: You can age adjust both D-dimer assays for appropriate patients with suspected pulmonary embolism. Link to age adjusted Calculator for both assays: MD Calc
Clinical Scenario: An 81-year-old female PMHx HTN, DM, remote history of breast cancer who presents to the ED with shortness for the past 2 days. She denies any recent fever, chills, or sick contacts. Patient has no history of DVT or PE. On exam, VS unremarkable except for a heart rate of 105. The resident identifies the patient as low-risk for PE via Wells score and orders a D-dimer. The attending is upset that the resident sent the test without telling them because “it’s always positive” but lets the resident ride it out. The D-dimer comes back “high” from the lab at 270 ng/mL. The resident asks the attending if we could age-adjust the D-dimer and end the workup for PE. What Your Gut Says: You can age adjust the D-dimer assay that other hospitals have, which have a cut off of 0.5 µ/mL or 500 ng/mL, but cannot be used in D-dimers with cutoffs of 230 µg/mL. Maybe in a different life or different hospital system this would work.
Background: D-dimer is a protein fragment found in the blood after a blood clot is broken down. This test is highly sensitive and can be used to “rule out” appropriate patients for Venous Thromboembolism (VTE). However, specificity is low, leading to a high number of false-positives and can increase the CTPA rate. D-dimer levels increase with age further reducing the specificity of the test in patients over 50. Most labs, and thus the vast majority of published studies, report D-dimer in fibrinogen equivalent units (FEUs). The common cutoff for this test is 500 ng/ml. Some laboratories use assays that report D-dimer units (DDU) where the cutoff is commonly set at 230 ng/ml. Thus, roughly 2 FEUs are equal to 1 DDU.
What The Evidence Says:
The Age-Adjusted D-dimer
There is strong evidence that we can safely use the age-adjusted D-dimer for appropriate patients for work up for VTE. Numerous studies have shown that using an age adjusted D-dimer could improve the specificity of the test while preserving its sensitivity. A summary of studies looking at the conventional D-dimer against the age-adjusted D-dimer was done by Wolf et al. showing comparable sensitivities for the conventional and age-adjusted values:
The 230 D-dimer Assay:
Though less studied than the FEU assay, there is growing evidence that the DDU assay can also be age-adjusted for appropriate VTE patients. All of the available data supports this approach:
- Parks et al: Investigation of age-adjusted D-dimer using an uncommon assay
This practice is supported by the ACEP guidelines on VTE:
Bottom Line: The available evidence supports the use of an age-adjusted D-dimer, with either assay (FEUs or DDUs), to rule out VTE in patients that are low risk by Wells criteria. The use of the age-adjusted D-dimers decreases the number of PE studies needed in the Emergency Department and does not significantly increase false negatives. Choose the appropriate assay when age-adjusting this test.
Bonus Pearls: The 230 µg/mL D-dimer Reference Card
Read More
REBEL EM: The YEARS Study – Simplified Diagnostic Approach to PE
REBEL EM:The Pragmatic Combination of YEARS Score and Age-Adjusted D-Dimer
References
American College of Emergency Physicians Clinical Policies Subcommittee (Writing Committee) on Thromboembolic Disease:; Wolf SJ, Hahn SA, Nentwich LM, Raja AS, Silvers SM, Brown MD. Clinical Policy: Critical Issues in the Evaluation and Management of Adult Patients Presenting to the Emergency Department With Suspected Acute Venous Thromboembolic Disease. Ann Emerg Med. 2018 May;71(5):e59-e109. Doi: 10.1016/j.annemergmed.2018.03.006. PMID: 29681319.
