Jennifer Schimmel, MD, on Urinary Antigen Testing for Diagnosing Pneumonia

Urinary antigen testing (UAT) is not routinely ordered for diagnosing pneumonia despite the associated opportunity for antimicrobial stewardship, according to the results of a recent study.1

This finding comes as part of a retrospective cohort study that analyzed data from 159,894 hospital admissions from 170 hospitals throughout the United States. The researchers sought to determine differences between the hospitals that use UAT, the relationship of UAT use to antibiotic de-escalation, and the outcomes of this association.

Study author Jennifer Schimmel, MD, who is an assistant professor of medicine at the University of Massachusetts Medical School, answered Infectious Diseases Consultant’s questions about the study findings and their implications.


Infectious Diseases Consultant: UAT is currently recommended by the Infectious Diseases Society of America (IDSA) for the diagnosis of pneumococcal infection. You and your colleagues posited that UAT could also be used for antibiotic de-escalation. How did this research question come about?

Jennifer Schimmel: We initially noted that a positive UAT was less frequently associated with the growth of organisms other than Streptococcus pneumoniae on culture. Other studies have shown that many patients with pneumonia are treated with broad-spectrum antibiotics. Since S pneumoniae does not usually require broad-spectrum antibiotics, from there it followed that a positive UAT could potentially be useful as a de-escalation tool on a larger scale. Since we also had access to antibiotic use data, we then looked at whether a positive or negative UAT influenced antibiotic decision-making.  

ID CON: For your study, your team retrospectively assessed 159,894 admissions to 170 US-based hospitals to better understand the variation in UAT use, associations of UAT results with antibiotic de-escalation, and associations of de-escalation with outcomes. Can you tell us more about the patient population and whether patient characteristics played a role in your results?

JS: Our study included 170 hospitals that participate in the Premier database. The hospitals are generally representative of US hospitals as a whole and include academic and nonacademic hospitals of various sizes located throughout the country. We included all patients with community-acquired pneumonia, including those admitted to the intensive care unit (ICU). We found that patient characteristics were much less important in determining who was tested than which hospital they went to. Rates of UAT testing ranged from 0% at some hospitals to 69% at the hospital with the highest rate. Patients in the ICU were a little more likely to be tested, which might be expected since the American Thoracic Society/IDSA guidelines recommend UAT be performed on patients with severe pneumonia.

ID CON: Overall, you found that UAT—the standard for diagnosing pneumococcal infection—is not routinely ordered in the ICU. In your opinion, what needs to be done in order to increase the use of UAT for diagnosing pneumococcal infection in the ICU?

JS: UAT is one way of diagnosing pneumococcal infection. Respiratory and blood cultures are another. The advantage of UAT is that it is faster and more sensitive. Since the guidelines already recommend UAT for patients in the ICU, it was disappointing that only about 1 in 3 patients in the ICU had it performed.

One limitation is that in some hospitals, UAT is (or was during the time of the study) a send-out test. Getting the test into more hospitals would likely help increase their use. Another hesitation about testing is that doctors may not act on the results. We found that doctors in hospitals that ordered the test more often were more likely to de-escalate therapy in response. That implies there is a cultural component that needs to be overcome. We hope that our work will make physicians feel more comfortable de-escalating therapy if the UAT is positive.

ID CON: You also found that positive UAT results were associated with less frequent resistant organisms but did not usually lead to antibiotic de-escalation. Do you think this de-escalation step should be added to the IDSA’s recommendations?

JS: In many cases, yes. It seems de-escalation based on a positive UAT would be a reasonable step. Although, our study was not able to make firm conclusions about the safety of doing so. There are situations such as with a more severely ill patient, who maybe even recently had S pneumoniae, where there still might be concern for a resistant organism despite a positive UAT, and de-escalation based on UAT would not be advisable.

ID CON: How can ICU physicians and other hospitalists better implement UAT for improved antimicrobial stewardship?

JS: Most likely, there would be more broad use if UAT was supported by national guidelines for the treatment of pneumonia. UAT is just one tool for antibiotic de-escalation, but it could be incorporated into practice with computerized order sets, with a reminder to order UAT possibly triggered for patients taking broad-spectrum antibiotics. Especially for patients for whom a positive UAT is thought to explain the etiology of their illness and are taking broad-spectrum therapy, UAT can be a useful tool to support antibiotic de-escalation and avoidance of unnecessary broad-spectrum antibiotics and their unintended consequences.



  1. Schimmel JJ, Haessler S, Imrey P, et al. Pneumococcal urinary antigen testing in united states hospitals: a missed opportunity for antimicrobial stewardship. Clin Infect Dis. 2020;71(6):1427-1434.