Hoping to reduce the frequency of unnecessary imaging in older patients, research published in the December issue of CHEST explored a sliding adjustment scale to D-dimer testing for pulmonary embolism.

The research team sought to determine if this adjustment to conventional D-dimer blood protein test thresholds would be a more efficient, effective and safe means of determining pulmonary embolism risk with the fewest false positive or negative responses. D-dimer concentration increases with age, creating increased false response rates with conventional testing, according to Scott C. Woller, MD, from the Eccles Outpatient Care Center at Intermountain Medical Center in Murray, Utah, and colleagues.

"If the protein levels are above a certain threshold, we most often order a CT scan to confirm or rule out a pulmonary embolism," Woller explained in a release.

Woller et al retrospectively analyzed 923 consecutive patient cases with available D-dimer testing results, revised Geneva score and CTPA follow-up. Particularly, these cases were identified as ones where patients were older than 50 years and unlikely to have pulmonary embolism by way of D-dimer testing and revised Geneva score.

They found that age-adjusted D-dimer testing was largely successful in validating patients who did not have pulmonary embolism. Age-adjusted D-dimer testing found 18 percent more patients negative than conventional testing. Among patients older than 75 years, age-adjusted thresholds reduced positive test rates from 95 percent down to 70 percent. Further, they found that comparing conventional and age-adjusted thresholds, significantly higher rates of negative D-dimer tests were seen when patients were grouped by age: between 51 to 65, 66 to 74, and 75 years or more, rates were 14.8 percent and 27.1 percent, 10.8 percent and 35.5 percent, and 5.1 percent and 30 percent, respectively.

However, they found the 90-day false-negative rates among patients older than 50 for the conventional against the age-adjusted test in this population was 0 percent and 1.5 percent. In patients 75 years and older, the false-negative rate was 2.7 percent.

While Woller et al supported the consideration of the age-adjustment for D-dimer testing, they noted that some of their findings may relate to being a retrospective instead of prospective study. They recommended further studies be conducted before using D-dimer testing age-adjustments in the clinical setting.