In this article an infectious diseases pharmacist discusses four diagnostic stewardship test areas that may be of interest to antimicrobial stewardship pharmacists.
AI Generated Summary:
This article highlights how certain commonly ordered diagnostic tests—such as the pneumococcal and Legionella urinary antigen tests, respiratory viral panels – often provide limited value in guiding antimicrobial decisions when used indiscriminately. It argues that applying principles of diagnostic stewardship can reduce unnecessary testing, improve patient care, and better support antimicrobial stewardship efforts.
Written By: Timothy P. Gauthier, Pharm.D., BCPS, BCIDP with minor assistance from ChatGPT
Article Posted 30 August 2025
Diagnostic stewardship refers to the coordinated and responsible use of diagnostic tests (e.g., labs, imaging) to ensure that the right test is ordered for the right patient, at the right time, and that the results are interpreted and applied correctly in clinical decision-making. Diagnostic stewardship is supposed to help avoid unnecessary diagnostic tests while improving the selection and efficiency of the ones that are needed. It can help reduce misdiagnosis, shorten time to accurate diagnosis, and minimize exposure to unnecessary medications.
Diagnostic stewardship is closely linked to antimicrobial stewardship, because establishing a diagnosis is the key step towards determining the right treatment. When a diagnosis is delayed the patient may get excessive therapies which do not align with antimicrobial stewardship principles. Faster diagnosis usually means better antibiotic stewardship. Sometimes stewardship programs can also collaborate with other folks (e.g., infection prevention and control, quality assurance and performance improvement, micro lab) to help promote good diagnostic stewardship through providing guidance and support related to tests used in the management of infectious processes.
It can be a fine line between having medication expertise and having diagnostic expertise, but certainly there are instances where infectious diseases pharmacists can support the diagnostic side of things. For example, I find blood and urine culture stewardship much more difficult for my pharmacist brain to digest as compared to something like MRSA nares stewardship which is more straightforward.
In this article I will highlight four areas in the realm of diagnostic stewardship that may be of interest for antimicrobial stewardship pharmacists, as we ask the question – are we doing this test for no reason? There are many other tests relevant to the topic, but here are some cliff notes, thoughts, and references for you to ponder about four.
1. Pneumococcal Urinary Antigen Tests
The Journal of Hospital Medicine has a fantastic series called “Things We Do for No Reason” and Open Forum Infectious Diseases also has an article with this in the title about this test. So do we do Pneumococcal (Streptococcus pneumoniae) urinary antigen test or “PUAT” for no reason? The concern is raised that these test results are often not clinically useful and when they are useful they may not make an impact. A negative PUAT does not definitely exclude S. pneumoniae infection and the tests are most often negative. When a PUAT is positive (which varies but is around 10% of the time) it tends to be reliable and can support more rapid antibiotic narrowing, yet that may be hampered by lack of clinician uptake.
IDSA/ATS CAP guidelines recommend considering PUAT selectively (not for routine use) when identification of pneumococcus would meaningfully impact therapy, for example potentially for severe CAP. The guideline gives it a conditional and low-quality recommendation. Its role is not to be applied universally, but selectively where results could justify narrowing therapy. So is it being over-used?
Here are a few readings about this topic:
◦ Things We Do for No Reason™: S. pneumoniae and Legionella urine antigen testing. 2025.
◦ ATS/IDSA Guidelines for Diagnosis and Treatment of Adults with Community-acquired Pneumonia. 2019.
2. Legionella Urinary Antigen Tests
While an argument can be made to completely remove PUAT testing, Legionella urinary antigen testing or “LUAT” is necessary for infection prevention and control programs to identify outbreaks. That stated, there seems to be a limited role for LUAT testing unless the patient has an appropriate clinical syndrome or exposure consistent with Legionella. The value of LUAT ordering has been called into question by many.
One thing I had not considered but learned was that a false-positive LUAT test can trigger an unnecessary investigation by infection control teams, which can mean substantial resource wastage. It breaks my heart to think those teams who already have so much important work to do could be sent on a wild goose chase.
Note too that a negative LUAT does not definitively exclude a Legionella infection.
Learn more about this topic here:
◦ Things We Do for No Reason™: S. pneumoniae and Legionella urine antigen testing. 2025.
◦ Diagnostic accuracy of urinary antigen tests for legionellosis: A systematic review and meta-analysis. 2022.
◦ Can we truly rely on the urinary antigen test for the diagnosis? Legionella case report. 2017.
◦ ATS/IDSA Guidelines for Diagnosis and Treatment of Adults with Community-acquired Pneumonia. 2019.
3. Rapid Diagnostic Testing for Respiratory Viruses
Thank you once again to the Journal of Hospital Medicine for another “Things We Do For No Reason” article! The issue here is that more elaborate panels for respiratory pathogens may provide a greater number potential viral and bacterial targets for identification, but compared to more simple tests targeting influenza, RSV, and SARS-CoV-2 alone, there may be no advantage gained in how patients are managed while the costs of care are increased.
It is notable on this topic that people in my circles who have no medical expertise have brought up their respiratory panel pathogen (RPP) results, because they asked for it by name after seeing it as an option during a Google search when their child was being treated for a viral bronchitis. I can see how denying a patient request for an RPP because it is not clinically appropriate could lead to patients satisfaction concerns. The societal or cultural component of care management applies to both antimicrobial stewardship and diagnostic stewardship. It can be tricky and should not be ignored.
It is also notable that the utility of more elaborate and expensive tests may be much greater in immunocompromised patients.
Here are some readings about this topic, I really like the second one from Antimicrobial Stewardship and Hospital Epidemiology, which provides an influenza-like-illness testing algorithm. The point-counterpoint article is also quite good.
◦ Diagnostic Stewardship of Respiratory Pathogen Panel Utilization. 2021.
◦ Respiratory pathogen panels in the hospital: good or unnecessary? 2017.
4. MRSA Nares Screening
Like most (if not all) infectious diseases pharmacists, I’m a total fan-boy of MRSA nares testing because it can potentially help us get people off of anti-MRSA antibiotics such as IV vancomycin. It tends to be an easy intervention for patients on empiric therapy for MRSA pneumonia. There has been greater interest in recent years for stopping anti-MRSA antibiotics beyond pneumonia, so people are now looking to get this test more often.
It leaves me wondering how many of these MRSA tests in hospitals are actually being used for their intended purpose? Is enthusiasm for non-pneumonia cases leading to wastage? Are some patients being tested more than once in a short time period? The pendulum is always swinging to and fro. Are we swinging the pendulum too far with MRSA nares testing? Will we see the Journal of Hospital Medicine publishing a future issue about over-ordering of MRSA nares in cases that do not have specific clinical syndromes where the data is robust enough to support therapy changes?
MRSA nares tests can have infection prevention and control implications. They are not free. It takes lab resources. The results are not always acted on. Do they have a role? Yes. However, MRSA nares testing also needs to be stewarded to ensure a reasonable balance between under-use and over-use.
Here are a few readings about MRSA nares:
◦ P-2090. Using MRSA Nares PCR to Predict MRSA Purulent Skin and Soft Tissue Infections. 2025
Closing Comments
As antimicrobial stewardship programs look to collaborate with team members to address diagnostic stewardship, there is great potential for synergy that results in better patient care. It is exciting that our interdisciplinary groups can have a meaningful impact on the healthcare system. Also, how nice is it that diagnostic stewardship efforts tend to align very well with regulatory requirements that promote integration between antimicrobial stewardship, infection prevention and control, and quality assurance and performance improvement!?!
For a fuller perspective beyond the article, readers should explore data on PUAT performance (sensitivity, specificity, positivity rates), guideline-recommended selective use, and studies showing how positive results can meaningfully drive antibiotic de-escalation. Many of these are available in the links provided above.
Have thoughts on this topic? Find me on social media @IDstewardship!
Disclosure: The views and opinions expressed in this article are those of the author and do not necessarily represent the position or policy of any past, current, or potential future employer.
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