Challenging the UTI Testing Gold Standard: PCR vs. SUC

Although women and older adults are most vulnerable, many people will experience a urinary tract infection (UTI) during their lifetimes. These common infections of the urinary system impact the kidneys, bladder, or urethra. In the United States alone, UTIs account for more than 8 million doctor visits each year [1]. Though not typically life threatening, UTIs can cause serious complications if left untreated and UTI-related hospitalizations cost an estimated $2.8 billion annually in the United States [2].

For patients with UTIs, antibiotics are the most prescribed treatment [3]. However, suspected UTI is one of the most common causes of inappropriate antibiotic prescribing in inpatient settings [4]. During a recent webinar, speakers from Acutis Diagnostics, Inc. discussed the benefits of polymerase chain reaction (PCR) testing for diagnosing UTIs compared to standard urine culture (SUC). Given the prevalence of UTIs, it’s important that patients receive the right diagnostic test so they can be prescribed the most appropriate treatment.

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Why the “gold standard” isn’t so golden

SUC is one of the most widely used diagnostic tests in healthcare and is currently considered the gold standard for diagnosing UTIs [5]. Still, this gold standard is not without its drawbacks, according to Dr. Becky Winslow, BS, PharmD, Clinical Science Liaison at Acutis. While presenting, Dr. Winslow dove into the challenges posed by SUC. “The standard urine culture was not actually validated for use in identifying lower urinary tract microorganisms. Yet for more than 60 years, the medical community has relied upon the standard urinary culture for identifying urinary pathogens,” said Dr. Winslow.

According to Dr. Winslow, urine cultures can result in a high number of false negatives. They are biased to grow E-coli, rather than detect slow growing organisms, fastidious and nonaerobic organisms, or most gram-positive organisms. Ultimately, the SUC can miss many bacterial species, which can prevent patients from being prescribed the appropriate treatment. Previous exposure to antibiotics can also skew a culture’s results, and polymicrobial infections can be misinterpreted as sample contaminations. Additionally, the SUC has a long turnaround time – taking up to 72 hours for a result.

“This has led to undiagnosed and misdiagnosed urinary tract infections, as well as antimicrobial resistance,” said Dr. Winslow.

The technical advantages of PCR testing

While the SUC is the current standard for UTI diagnosis, PCR testing offers key advantages. For one, PCR has a faster turnaround time than SUC. PCR tests, unlike the SUC, are also not dependent on bacteria growth in culture to detect and identify infection. This makes PCR more accurate, explained Dr. Winslow, as it’s able to pick up on an infection where a SUC might instead produce a false negative.

Dr. Winslow presented a retrospective record review of 582 elderly patients who presented with symptoms of lower UTIs demonstrating that PCR is more accurate for UTI testing than SUC. Although all patients received urine cultures and PCR molecular testing, there were discrepancies in the positive and negative cases reported by each diagnostic. For example, PCR found uropathogens in 56% of samples, while culture detected them in only 37%. In one of four (26%) of cases results were discordant. “These results suggest that PCR may be likely to identify pathogens before traditional culture will,” said Dr. Winslow.

Furthermore, polymicrobial infections were detected in 12% of samples where the culture delivered a negative test result. Without a PCR test, this means those patients may have been missed or treated for UTI when they had a different infection.

Taking a closer look at the patient journey

If a patient presents with signs and symptoms of a lower UTI, explained Dr. Winslow, their doctor will then perform a urinalysis (UA) at the office. From there, depending on UA results, the sample will typically be sent for SUC. If PCR is performed instead, results are typically available sooner than with SUC. According to Dr. Winslow, this leads to a faster decision to prescribe or deescalate, which can benefit antimicrobial stewardship.

Dr. Mayil Shanmugam, PhD, Senior Scientist at Acutis, also joined the webinar to share an overview of the rigorous validation and regulatory process for PCR diagnostics. Tests are validated for specificity, including inclusivity and exclusivity, as well as sensitivity, precision, accuracy, and stability, said Dr. Shanmugam.

For Dr. Winslow, the connection between UTI diagnostic stewardship and fighting antimicrobial resistance is clear: “By choosing a rapid diagnostic test for urinary-tract infections and having the right result reported, as well as the right interpretation, and right antimicrobial at the right time, [this] will lead to better outcomes and antimicrobial stewardship.”

To learn how polymerase chain reaction (PCR) testing may be advantageous compared to standard urine culture (SUC) for identifying uropathogens, watch the free webinar on-demand.

For information on Thermo Fisher Scientific solutions that facilitate research in UTIs, please click here.

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