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New Algorithm Helps Diagnose Pulmonary Embolism in Older Patients

October 9th, 2016

SALT LAKE CITY – A new sliding scale model is more accurate than current diagnostic methods in helping emergency physicians rule out pulmonary embolisms in older patients, according to a recent study.

The new model factors in patient age and more accurately identifies a patient's risk of potentially fatal blood clots, according to the research published recently in the journal CHEST. That can avert the need for additional, more invasive tests and help reduce unnecessary costs, according to the study led by researchers from Intermountain Medical Center in Salt Lake City.

Background in the article notes that pulmonary embolism is associated with more deaths annually than breast cancer, HIV/AIDS, prostate cancer, and motor vehicle accidents combined.

"When patients come to the ER with the symptoms of a pulmonary embolism, we begin by doing a physical exam and identifying their previous medical history," explained lead author Scott Woller, MD, co-director of Intermountain Medical Center's Thrombosis Program. "Once we get that initial information, we often conduct a simple blood test called a d-dimer, which tests for proteins found in the blood when a clot is present. If the protein levels are above a certain threshold, we most often order a CT scan to confirm or rule out a pulmonary embolism. However, as we age, D-dimer levels naturally increase, which means when we test D-dimer in elderly patients, we often find an elevated result – even when a clot is absent. This is referred to as a false-positive test."

Looking at more than 900 patients who presented to the ED with symptoms of a pulmonary embolism (PE) and had D-dimer tests ordered, researchers determined that adjusting the threshold of D-dimer levels in correlation to a patient's age accurately excluded a pulmonary embolism diagnosis without requiring additional testing.

While the conventional cutoff used to identify a normal D-dimer value is 500, researchers suggest that patients older than 50 should have the cutoff adjusted upward to a value equal to the patient's age multiplied by 10. For example, a 72-year-old patient would have a normal D-dimer value of less than 720.

No PEs were found within 90 days among 104 patients with a negative conventional D-dimer test result and a Revised Geneva Score equal to or less than 10, according to the results. Among 273 patients with a negative age-adjusted D-dimer result and an RGS equal to or less than 10, four PEs were observed within 90 days.

"A CT scan is most often used to ultimately rule out a pulmonary embolism, however it delivers radiation to the patient and contrast dye," Woller pointed out. "Elderly patients are at greater risk for inadvertent harm related to the CT scan, and the contrast dye may also impact kidneys function, plus the scan adds to the cost of the patient's care. If we can safely and accurately diagnose the patient's risk of a pulmonary embolism using this sliding D-dimer scale, we can eliminate the need for additional imaging tests."

The study notes that adoption of the age-adjusted cutoff would decrease the number of CT scans that would need to be performed by nearly 20%. More studies are being conducted to verify the accuracy of the sliding scale.

“Use of an age-adjusted D-dimer threshold reduces imaging among patients aged > 50 years with an RGS ≤ 10,” study authors conclude. “Although the adoption of an age-adjusted D-dimer threshold is probably safe, the CIs surrounding the additional 1.5% of PEs missed necessitate prospective study before this practice can be adopted into routine clinical care."