By Gabrielle Gleeson-Solomon, CEO of Tota
Scientific Review by Dr Nick Parkinson, PhD
On UTI testing and what a 'negative' test really means.
There's a particular kind of dread that comes with feeling a UTI coming on... The stinging, the constant trips to the bathroom, the cancelling plans and trying to work out how quickly you can get hold of antibiotics.
So you do everything right. You chase a same-day GP appointment, or get seen by a pharmacist, or buy something over the counter to take the edge off until someone can help. Then one of two things happens. Either nobody tests you at all because your symptoms are enough to prescribe antibiotics, or you get the frustrating result so many women fear: UTI symptoms but urine test negative.
Nothing there. No infection. Except you know something's there, because you can feel it.
We’re here to tell you, you aren’t imagining it. Around half of women will have a UTI at some point, and roughly one in ten will go on to have recurrent bouts. That works out at approximately 700,000 chronic and recurrent cases a year in the UK alone.
If you're experiencing UTI symptoms but your test is negative, it doesn't always mean there's nothing wrong. Quite often it means the test failed to find what’s actually going on.
What actually happens to your sample
Most UTI testing in the UK is done by a midstream urine culture. A sample of your urine gets spread onto a culture dish and left in a lab. If bacteria are present in big enough numbers and happy with the conditions, they form visible colonies that the lab can identify.
The catch is that plenty of bacteria don't grow that way. Some are slow. Some don't like oxygen. Some just need conditions that culture dish isn't offering.
When researchers have compared the standard culture against more in-depth methods, they found the standard test missed around two thirds of the bacteria which might be causing infections. In women with chronic UTIs, it missed roughly nine in ten.
This means what appears to be a negative UTI test doesn't necessarily rule out an infection. It tells you that nothing grew under those laboratory conditions. There could still be bacteria in the sample causing symptoms.
How many bacteria count as an infection?
Even when bacteria do grow in those standard urine cultures, there’s a second hurdle. Most labs will only report a positive urine culture if there are 100,000 bacteria per millilitre of urine. Below that, the result is reported as negative.
But that threshold was set in 1956 by a researcher called Edward Kass. He was working with pregnant women, trying to tell a genuine kidney infection apart from a sample that had picked up bacteria on the way into the pot. For that specific job, it was sensible to draw the line at a high number. The 100,000 threshold was never intended to define the infection level for every woman with UTI symptoms, forever.
Since then, research has repeatedly shown that women with UTI symptoms often have far fewer bacteria than that, sometimes as few as 100 per millilitre.
So the threshold for a positive urine culture is a thousand times higher than the level many symptomatic women actually have.
There's another reason standard urine cultures can miss infections
There's a third way things get missed when it comes to standard urine cultures. Sometimes several different bacteria grow in the dish at once, and labs often report this as "mixed growth”. In practice that tends to be treated much like nothing growing at all, on the basis that the sample may have picked up bacteria during collection.
The problem is that infections involving more than one organism are common, particularly in women whose UTIs keep coming back. So the women who most need an answer can be the ones most likely to have theirs put down to a dodgy sample.
What about over the counter tests?
These are simple dip stick tests. You dip into a urine sample and see whether it changes colour. These work by looking for two chemical clues: nitrite, which some bacteria produce, and leukocyte esterase, a sign that immune cells are present.
They’re fast and cheap. However, the nitrite test on its own misses around half of bacterial UTIs and it’s unreliable for several common bacteria.
Dipstick tests are quick and convenient, but they're also one of the least accurate ways to diagnose a UTI because they rely on indirect chemical clues rather than identifying the bacteria themselves.
That's why dipsticks are best thought of as a quick screening tool rather than a definitive UTI test.
What if your UTI symptoms persist but the test is negative?
If you've been experiencing burning pee but no infection has been found, this may help explain why your symptoms haven't matched your test results.
A negative standard test does not fully rule out an infection. So if symptoms are still there, there are two main possibilities for what’s going on:
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There may be bacteria present that the standard culture did not pick up and could be contributing to your symptoms.
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It's also important to remember that bladder pain but a urine test that's clear can have causes other than a bacterial UTI, which is why further investigation may sometimes be needed.
A urinary microbiome test takes a different approach. These tests use DNA sequencing to read the full genetic material in a sample to identify all the bacteria and fungi present, this includes organisms that can’t grow in a standard urine culture. It also shows how much of each organism is present, which research suggests matters for whether organisms might be contributing symptoms or not.
The symptoms are real
The test most women are given was designed in the 1950s, before anyone knew the urinary tract had a microbiome at all. The science has moved on considerably since then. Today, we can learn far more about what's happening in the urinary tract than standard urine cultures were ever designed to show.
Sources
- Foxman B. Epidemiology of urinary tract infections: incidence, morbidity, and economic costs. Am J Med. 2002;113 Suppl 1A:5S-13S. PubMed: 12113866
- National Institute for Health and Care Excellence (NICE). Urinary tract infection (lower) – women: Background information – Prevalence. Clinical Knowledge Summaries. NICE CKS
- Price TK, Dune T, Hilt EE, Thomas-White KJ, Kliethermes S, Brincat C, et al. The clinical urine culture: enhanced techniques improve detection of clinically relevant microorganisms. J Clin Microbiol. 2016;54(5):1216-1222. PubMed: 26962083
- Sathiananthamoorthy S, Malone-Lee J, Gill K, Tymon A, Nguyen TK, Gurung S, Collins L, Kupelian AS, Swamy S, Khasriya R, Spratt DA, Rohn JL. Reassessment of Routine Midstream Culture in Diagnosis of Urinary Tract Infection. J Clin Microbiol. 2019 Feb 27;57(3):e01452-18. PubMed: 30541935
- UK Health Security Agency / NICE. Diagnosis of urinary tract infections: quick reference tools for primary care. GOV.UK. GOV.UK
- Tullus K. Defining urinary tract infection by bacterial colony counts: a case for less than 100,000 colonies/mL as the threshold. Pediatr Nephrol. 2019;34:1651-1653. Springer
- Advani SD, Thaden JT, Perez R, Stair SL, Lee UJ, Siddiqui NY. State-of-the-art review: recurrent uncomplicated urinary tract infections in women. Clin Infect Dis. 2025;80(3):e31-e42. PubMed: 40095960
- Devillé WLJM, Yzermans JC, van Duijn NP, Bezemer PD, van der Windt DAWM, Bouter LM. The urine dipstick test useful to rule out infections. A meta-analysis of the accuracy. BMC Urol. 2004;4:4. PubMed: 15175113
This article is for general information and does not replace medical advice. If you're experiencing new, severe, persistent or worsening symptoms, please speak to a GP or another qualified healthcare professional.
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