New research from Belgium suggests that the standard culture test for bacteria may return a negative result even though the patient tested actually has a urinary tract infection. The study compared women with symptoms of urinary infection - such as pain during urination and feeling an urgent or frequent need to urinate - with non-symptomatic women. With the help of a more sensitive test, it found that nearly all the symptomatic women with a negative standard test result actually did have an infection.

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Research has shown that the standard test for diagnosing UTI may mistakenly return negative results.

The study - by researchers from Ghent University and Ghent University Hospital in Belgium - is published in the journal Clinical Microbiology and Infection.

Urinary tract infection (UTI) is one of the most common infections that people experience. It arises when bacteria - most likely from the skin or rectum - enter the urethra and travel up to the bladder.

Lead author Dr. Stefan Heytens, a researcher at Ghent University and a practicing GP, says that their findings support the idea that, for women with symptoms of an uncomplicated UTI, there is no need to carry out a standard culture test.

"A substantial percentage of women visiting their GP with symptoms of a UTI, who test negative for a bacterial infection, are told they have no infection and sent home without treatment," Dr. Heytens comments.

"On the other hand," he adds, "women with a positive test might be given a short course of antibiotics to treat their infection."

Standard test is negative for many symptomatic women

UTIs affect several parts of the urinary tract, which includes the urethra, bladder, ureters, and kidneys. However, the most common type of UTI is a bladder infection, also known as cystitis.

Fast facts about UTI
  • Research suggests that between 40 and 60 percent of women have a UTI during their lifetime.
  • Bladder infection is the most common type of UTI.
  • In a few cases, the UTI can spread to one or both kidneys.

Learn more about UTI

The symptoms of UTI include experiencing a burning feeling during urination, or having frequent and intense urges to urinate, even when there is not much urine to pass.

Females are more likely to be affected by UTIs than males because they have a shorter urethra that is closer to the anus, making it easier for bacteria to get into the urinary tract and cause infection.

In the United States, UTIs account for more than 8.1 million visits to healthcare professionals every year.

Dr. Heytens and colleagues note that around 20 to 30 percent of women with symptoms of UTI who have the standard culture test have a negative result.

The standard culture test involves sending a urine sample to a laboratory, where it is cultured and tested to determine the types of bacteria present, if any.

Negative standard test 'assumed to mean no UTI'

If the result of the standard test is positive, then the patient may be offered a course of antibiotics. These can include fosfomycin, nitrofurantoin, or trimethoprim.

However, the researchers say that many doctors assume that if the test result is negative, then the patient does not have a UTI.

They note that there has also been a tendency, in the past, to consider women who fall into this category as having unexplained 'urethral syndrome', and that the cause is likely to be psychosomatic.

For their study, Dr. Heytens and colleagues compared urine samples from 220 women who went to see their doctor because they had symptoms of UTI, with those of 86 healthy women with no such symptoms.

The urine samples underwent the standard culture test and were also tested with a more sensitive method called quantitative polymerase chain reaction (qPCR), which can detect minute amounts of bacterial DNA known to cause UTIs, including Escherichia coli and Staphylococcus saprophyticus.

'If a woman has symptoms, she probably has a UTI'

The researchers found that the standard test detected bacteria in 80.9 percent of urine samples from the symptomatic women.

However, the qPCR test detected E. coli in 95.9 percent of those samples, and S. saphrophyticus in 8.6 percent.

When the two qPCR test results were combined, they showed that 98.2 percent of the symptomatic women had an infection.

In the symptom-free, healthy volunteers, the standard test found evidence of E. coli in 10.5 percent of them, and the qPCR test found E. coli in 11.6 percent.

Dr. Heytens says that the more sensitive qPCR test found evidence of E. coli in the urine samples of nearly all the women presenting with UTI symptoms, even when their standard test returned a negative result.

"This suggests that if a woman has these symptoms, she probably does have a UTI," he suggests, and concludes:

"Our findings support previous research which indicates that traditional testing may not be helpful in uncomplicated UTIs. However, traditional urine culture tests may still have a role to play if treatment fails or if there are signs and symptoms of a more complicated UTI."

However, he also points out that they still do not know if antibiotics are of benefit to all women who present with UTI symptoms.

Also, he and his colleagues caution that their results should now be replicated by further studies. In the meantime, they wish to explore the potential for qPCR as a test for other types of bacteria that can cause UTI.

Learn about causes and treatment of frequent urination in women.