Kaiser Permanente study findings could help clinicians identify pregnant patients who can safely avoid advanced imaging tests
A common, inexpensive blood test used to detect evidence of a pulmonary embolism — a blood clot in the lung — can determine which pregnant patients experiencing chest pain or trouble breathing can safely avoid additional advanced imaging tests, new Kaiser Permanente research suggests.
“Advanced imaging tests, like CT scans, can be used to diagnose a pulmonary embolism, but they add additional time and risk to a patient’s evaluation,” explained first author David Vinson, MD, an adjunct investigator at the Kaiser Permanente Division of Research and an emergency medicine physician with The Permanente Medical Group (TPMG). “Our study shows there is no need for every pregnant patient who might have a pulmonary embolism to have a CT scan when a D-dimer blood test — coupled with a simple decision aid — can identify a large proportion of patients for whom a CT scan is unnecessary.”
The study, published in JAMA Network Open on November 4, included 699 pregnant patients who were evaluated for a pulmonary embolism at a Kaiser Permanente Northern California hospital from October 2021 to March 2023 with a D-dimer blood test, compression ultrasound, a CT scan, or a perfusion scan, which measures blood flow in the lungs.
The researchers analyzed 720 patient visits. (Some of the patients experienced difficulty breathing or chest pain more than once.) There were 620 visits in the emergency department, 84 in the labor and delivery unit, and 16 in outpatient clinics. Overall, 315 patients had advanced imaging (defined as either a CT scan or perfusion scan), and 5 were diagnosed with a pulmonary embolism.
Our findings suggest there may be more opportunities for clinicians to use this test when they suspect a pregnant patient might have a pulmonary embolism.
— Nareg Roubinian, MD
The study found that 534 (73%) of the patients were evaluated with the D-dimer blood test. This test looks for the D-dimer protein fragments that blood clots release. D-dimer is normally a low value in the blood; an elevated value may indicate a blood clot is developing or breaking down. The study found that 30% of tested patients had a normal D-dimer value, 96% of whom were not referred for a CT scan. One-third had a slightly elevated D-dimer value, which can be normal in pregnancy, and about half of these were safely able to avoid CT imaging.
Overall, 229 (32%) of the pregnant patients had a compression ultrasound of the leg, a test that can identify a blood clot (called a deep vein thrombosis), which can be a precursor to a pulmonary embolism. Within this group, 3 (1%) were found to have a deep vein thrombosis. All the clots were identified in patients who had suggestive symptoms, like pain and swelling in one leg more than the other. No patients without pain or swelling in one leg had a deep vein thrombosis. The researchers say that the findings confirmed compression ultrasounds should be reserved for patients with suggestive symptoms, consistent with recommendations in multiple practice guidelines.
“Pregnancy increases the risk of blood clots, and missing a pulmonary embolism in a pregnant patient can result in severe complications, including death,” said study co-author Jeffrey Sperling, MD, MS, a maternal-fetal medicine specialist with TPMG. “Shortness of breath and chest discomfort are common in pregnancy, so clinicians need reliable tools to distinguish symptoms that are normal from those that are life threatening. This means it’s important to both identify patients with pulmonary embolism as well as avoid unnecessary radiation exposure from imaging, because it carries potential risks for the pregnant patient and their baby.”
Opportunities for expanded use
Previous studies showed the D-dimer test reduced advanced imaging by up to 39% by ruling out a pulmonary embolism in pregnancy. The new study builds on that research.
“For years, clinicians have been using D-dimer to identify non-pregnant patients at such low risk for pulmonary embolism that they can safely forgo CT imaging,” said Vinson. “Recent studies have shown the test was also effective in pregnant patients. Our study confirms this finding.”
The researchers noted that their study also found that the D-dimer blood test was more than 3 times as likely to be used in the emergency department than in the labor and delivery unit. It was also more likely to be used to rule out a pulmonary embolism in pregnant patients in their first trimester than it was in those in their third trimester. This suggests there may be more opportunities for clinicians to use the D-dimer blood test when they suspect a pregnant patient might have a pulmonary embolism.
“We did this study because no one knew how often these tests were being used in the community setting to keep pregnant patients from having unnecessary advanced imaging tests,” said senior author Nareg Roubinian, MD, an adjunct investigator at the DOR and an intensive care doctor with TPMG. “Our findings suggest there may be more opportunities for clinicians to use this test when they suspect a pregnant patient might have a pulmonary embolism, regardless of how far along they are in their pregnancy and whether they are in the emergency department or in the labor and delivery setting.”
Added Vinson, “Any pregnant patient with symptoms suggestive of a pulmonary embolism, like increased shortness of breath or chest pain, should seek medical care. These patients should also know that if advanced imaging, like a CT scan, is recommended, they should ask that a D-dimer test be used first to see if the CT scan is necessary.”
The study was supported by Kaiser Permanente Community Health and The Permanente Medical Group Delivery Science and Applied Research Program.
Co-authors include Madeline J. Somers, MPH, and Mary E. Reed, DrPH, of the Division of Research; Lara Zekar, MD, and Cydney E. Middleton, MD, of UC Davis Health; Edward Qiao, BS, of the California Northstate University School of Medicine; and Sara T. Woldemariam, MD, Nachiketa Gupta, MD, PhD, and Luke S. Poth, MD, of The Permanente Medical Group.
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About the Kaiser Permanente Division of Research
The Kaiser Permanente Division of Research conducts, publishes, and disseminates epidemiologic and health services research to improve the health and medical care of Kaiser Permanente members and society at large. KPDOR seeks to understand the determinants of illness and well-being and to improve the quality and cost-effectiveness of health care. Currently, DOR’s 720-plus staff, including 73 research and staff scientists, are working on nearly 630 epidemiological and health services research projects. For more information, visit divisionofresearch.kp.org or follow us @KPDOR.
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