Is it time to rethink midstream urine culture for UTI diagnosis?

Evelyn Lewin

25/06/2019 3:07:10 PM

Research shows that an MSU may be unsuitable for excluding UTIs in patients with lower-urinary-tract symptoms.

Asking for urine sample
The study found that MSUs miss ‘a significant proportion’ of bacteria.

Midstream urine culture (MSU) is currently seen as the gold standard test for diagnosing a urinary-tract infection (UTI) in adults.
However, a recent study published in the Journal of Clinical Microbiology is questioning whether it should remain in top position.
The study looked at urine specimens from 33 patients with chronic lower-urinary-tract symptoms (LUTS) attending their first appointment, 30 LUTS patients on treatment whose symptoms had relapsed, and 29 asymptomatic controls.
Researchers compared the bacterial enrichment capabilities of the MSU culture with those of a 50 µl uncentrifuged culture, a 30 ml centrifuged sediment culture, and 16S rRNA gene sequencing.
‘We showed that the routine MSU culture, adopting the UK interpretation criteria tailored to acute UTI, failed to detect a variety of bacterial species, including recognised uropathogens,’ the authors wrote.
They concluded the diagnostic MSU was unable to discriminate between patients and controls.
‘This work put the MSU head-to-head with modern DNA analysis methods – and it failed spectacularly,’ researcher Dr Jennifer Rohn, head of Urological Biology at University College London’s Department of Renal Medicine in the Division of Medicine at the Royal Free Hospital, said.
‘On the other hand, genomic sequencing using enriched urine specimens easily managed to pick out people who were genuinely ill.’
As part of the study, researchers found that fewer than 10% of patients with a clinically suspected UTI had a positive MSU, with only four of 33 new patient cultures producing non-microbial growth at 105 CFU/ml.
In contrast, bacterial DNA sequencing revealed bacteria, including recognised uropathogens, in 32 new patients. These included symptomatic patients who were reported to have a negative MSU.
In conclusion, the study found that the MSU protocol ‘misses a significant proportion of bacteria’.
The researchers therefore state that an MSU ‘may be unsuitable for excluding UTI in patients with LUTS’ and advise that those responsible for UTI detection, diagnosis and patient care ‘may wish to use caution when interpreting a negative or mixed-growth MSU in symptomatic patients’.
Dr Rohn said MSUs have been under suspicion as a diagnostic test for some time.
‘We’ve had inklings of this for years,’ she said. ‘This really proves it for the first time.’
Dr Rohn said embarrassment and stigma about UTIs, as well as with conservative thinking in medicine, may be among the reasons this issue has remained in the background.
‘I feel like it’s been neglected in medicine because these people have been neglected,’ she said.
‘It’s really sad. People tell these same stories, “I’m begging for antibiotics, I’ve had symptoms for 10 years but the computer says no. The test is negative”.
‘I feel it’s a moral issue in a way, that patients are getting a bad deal.’
This is not the first study to question the usefulness of the MSU in detecting UTIs.
Research published in the Journal of Clinical Microbiology in May 2016 found that, compared to the expanded-spectrum enhanced quantitative urine culture (EQUC), the standard urine culture missed 67% of all detected uropathogens and 88% of non-E.coli uropathogens.
Professor James Malone-Lee is a world leader in the study of chronic UTIs who worked on the most recent research. He is also critical of the diagnostic abilities of the MSU.
‘The test we currently use for urinary-tract infections is primitive and has never been properly validated,’ he said.
‘We’re still using the same test we were using 70 years ago.’
Along with questioning the idea of whether MSU is the best test to detect UTIs, Professor Malone-Lee also believes UTIs can be chronic. He said patients with chronic UTI may have bacteria that get inside the lining of the bladder and therefore cannot be detected in urine, making MSU obsolete as a diagnostic tool.
In such cases, Professor Malone-Lee said long-term (even up to six years’ worth) maximum dose of first-generation urinary antibiotics may be needed.
Many factors dictate what test to use in diagnosing UTIs, including cost, effectiveness, ease of access, and more.
So what should GPs do if they suspect a patient has a UTI, but the MSU comes back negative?
‘We should be looking harder if people get a negative result but present with UTI symptoms,’ Alexandra Mowat from the UroGynaecological Society of Australia said.
‘In highly resourced clinics, we can ask the microbiologists to look for the DNA of certain bacteria which are hard to cultivate but that are known to cause bladder symptoms, such as gonorrhoea, chlamydia and mycoplasma.’
Meanwhile, Dr Rohn believes that when it comes to MSUs, ‘We urgently need to develop alternative rapid diagnostic tests to take its place’.
According to Kidney Health Australia, around one in two women and one in 20 men will get a UTI in their lifetime.

midstream urine culture urinary tract infection UTIs

newsGP weekly poll Which public health issue will most significantly impact general practice in Australia in the next 10–20 years?

newsGP weekly poll Which public health issue will most significantly impact general practice in Australia in the next 10–20 years?



Login to comment

Jayne Ingham   26/06/2019 7:36:16 AM

I find hiprex helps those people with ongoing symptoms of UTIs. They complain about the size of the tablet.

Dr Felicia Caroline Higgins   26/06/2019 10:28:35 AM

So we should treat the patient, not the test result? How novel..........

Dr Viviane Sarah Leventhal   26/06/2019 11:31:30 AM

very useful . thank you .Which Labs do the the genetic sequencing ? or should I be researching this myself ?

Dr Horst Paul Herb   27/06/2019 8:46:25 AM

Unfortunately a very small study with doubtful statistics, but raising many important concerns. For now, I guess, we keep doing what we always have: treating the patient, and taking tests into consideration in the context of the clinical presentation.
One of the reasons why we won't be replaced by machines or lesser trained professions any time soon.

Dr Joveria Javaid   28/06/2019 6:47:32 AM

Dr Herb you summed it up quite well.

Peter   29/06/2019 11:02:30 AM

How about the antibiotic sensitivity. MSU may miss mild UTI but unlikely miss the severe cases. The antibiotic resistance is more important issue.

Chris Lawson   29/06/2019 1:55:19 PM

The study looked at patients presenting to a chronic LUTS hospital clinic. This is very different to the common GP presentation for acute LUTS. In GP, it is typical to start empirical treatment on the day of presentation rather than wait for culture. Although some experts advise against routine MSU for uncomplicated UTI, I order them so that if the patient does not respond I can check antibiotic sensitivities. PCR will not give antibiotic sensitivities (maybe one day, but these are not yet part of laboratory PCRs). Adding PCR would only be of use to me for patients who present several times with UTI symptoms and negative MSU and who don't respond to empirical antibiotic therapy. This is a very, very small subset.

I expect routine PCR would increase the financial burden of UTI pathology testing considerably.

Dr David Alan White   2/07/2019 9:53:37 PM

woudn't pyuria still show up even if the bacteria where inside the bladder wall?

Russell D'Cunha   7/07/2019 3:57:32 PM

This was an interesting read and quite topical as I am a big user of midstream urine MCS as a GP Registrar. Mainly I am using the sample to confirm the diagnosis + determine antibiotic susceptibility in case of failure to respond to empirical therapy (usually either cephalexin or trimethoprim are my first-line go-to agents).

However, I have noticed on average approx 50% of my MSU's return a "no growth" result. Which in light of this article makes me wonder whether sending off an MSU is worth the costs to the system considering I am deciding to treat clinically anyway?

That said, I do get the occasional positive but resistant UTI where the sample has been useful, and on a few occasions have detected some less common UTI pathogens such as salmonella (which the lab report states automatically gets referred to the local public health unit).

Lauren   25/07/2019 7:41:42 PM

About time this made it into the mainstream. I am a patient of professor malone Lee in london, after exhausting all avenues in Australia, and being diagnosed with incurable IC. I had worsening symptoms and negative MSUs for a year before moving bavk to the UK for treatment. I am now symptom and antibiotic free and living a normal life. I quite literally owe my life to Professor Malone Lee, as I was housebound, unable to work and in constant pain before I met him.

The tests are outdated! Many thousands of women (and men) are living in pain for years, decades! This needs attention.

Dr. Mark Karaczun   16/08/2019 5:43:27 AM

Potentially helpful. Locally, our stool cultures now just report PCR against a list of key pathogens rather than the old culture results which used to take ages. Having something similar may be helpful for urines, especially if they are reported more quickly. Positive samples can perhaps then be cultures for sensitivities. More MSUs rather than less may help build a better epidemiological picture which could better inform antibiotic prescribing.