A recent study entitled “Assessment of the Safety and Efficiency of Using an Age-Adjusted D-dimer Threshold to Exclude Suspected Pulmonary Embolism” suggests that adjusting the value of d-dimer test according to patients age is a safe and accurate method to determine patients with pulmonary embolism. The study was published in the journal CHEST.

Pulmonary embolism (PE) is characterized by the blocking of one (or more) arteries in the lungs, and is usually caused by blood clots that reach the lungs’ vasculature from other body parts, such as the legs. If left untreated, PE is fatal, but with appropriate and rapid treatment, the risk of death is significantly diminished. However, the clinical phenotype of PE can be variable. Currently, the diagnosis of PE is performed by determining patients’ risk factors and with a blood test, the D-dimer. The D-dimer test measures the presence of a protein associated with blood clots and thus is used to determine PE, among other syndromes, such as deep venous thrombosis (DVT) or disseminated intravascular coagulation (DIC). However, in the case of PE, since the D-dimer specificity is low, patients’ diagnosis has to be confirmed with CT pulmonary angiography. Notably, with age, the levels of d-dimer tests increase, thus a d-dimer test alone can predict PE when in the reality there is no blood clot.

In this study, a team of researchers at the Intermountain Medical Center in Salt Lake City proposed to determine the safety of adjusting a D-dimer threshold according to age. The authors studied 923 patients who were at least 50 years old that were admitted to the emergency room with a suspicion of PE. As a standard protocol, the patients were submitted to d-dimer tests and CT pulmonary angiography. After confirming the false-positive cases, the authors compared the standard d-dimer test results with an adjusted D-dimer threshold according to patients’ age. They observed that this adjusted value was accurate in excluding false-positive PE diagnosis without the necessity of further confirmation by other tests. Specifically, the team of researchers propose an adjusted-value determined by multiplying a patient’s age by 10, therefore, a patient who is 75 years old has a normal d-value if it is below 750 (the standard d-dimer test sets the normal cutoff at 500).

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These results suggest that in patients above the age of 50, the age-adjusted value of the d-dimer test is reliable and it prevents the necessity for CT scans to diagnose those at risk of PE. This method, a “sliding scale,” is now under further investigation.

Scott Woller, MD, co-director of Intermountain Medical Center’s Thrombosis Program and the study’s first author commented, “A CT scan is most often used to ultimately rule out a pulmonary embolism, however it delivers radiation to the patient and contrast dye. 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.”