Blood in the urine: when and how to investigate

You saw pink, red or brown urine. Maybe it happened once and then went back to normal. Maybe there was no pain either, and that made you think it must be nothing important. This article explains what reliable sources say, without frightening you and without making light of it.

What does it look like, and what can cause it?

The NHS says blood in the urine may be light pink, red or dark brown, and that even if the amount is small or you are not sure it is blood, it should be checked. The blood comes from the bladder, kidney or urethra. The same page lists three common causes: a urinary infection (burning when you urinate, frequency, smelly or cloudy urine, fever or flank pain), a kidney stone (severe, coming-and-going pain in the flank, back or groin, with restlessness and nausea), and an enlarged prostate in men over 50 (difficulty urinating and waking at night). Sometimes there is no blood at all: beetroot and some medicines change the colour, and bleeding from the rectum or a period can be mistaken for it.

Two kinds of blood in the urine

The first kind you can see with your eye. The second is found only in a test. For this microscopic type (microhematuria), the AUA/SUFU guideline sets the threshold at three or more red blood cells per high-power field in one sample.

A 2023 systematic review built from the evidence behind that guideline writes that asymptomatic microhematuria is very common and the associated risk of cancer of the urinary tract and upper tract is low. For this reason, instead of one pathway for everyone, the guideline sorts patients by their risk.

Why is “no pain” not reassuring?

On its bladder cancer page the NHS says the main sign is blood in the urine, and that any blood, even without another sign, even if it is the first time or only a little, should be checked promptly. Pain goes more with stones and infection, and its absence does not rule out other causes. The NHS also says blood in the urine can be a sign of cancer, which is easier to treat if found early. This does not mean “it is probably cancer.” The NHS writes in the same place that having these signs does not mean you definitely have bladder cancer, and the same goes for being referred to a specialist.

One point to gauge the size of the risk: the EAU writes that smoking is the most important risk factor for bladder cancer and explains about 50 percent of cases, and the risk rises with the duration and amount smoked. If you smoke or have smoked, tell your doctor.

What does the assessment usually involve?

The NHS says the doctor asks about your symptoms, may do a rectal or vaginal examination, may ask for a urine sample or blood test, may give antibiotics if infection is likely, and refers you if needed. A urine test and culture to find out whether there is an infection is the first step. How to give a sample is described in the test preparation guide.

For microhematuria, the AUA/SUFU guideline (2020) says to sort the patient into a low, intermediate or high risk group for urinary tract cancer. The criteria include age, sex, smoking and other risk factors, the amount and persistence of blood, and any history of visible blood. Cystoscopy (looking inside the bladder with a thin camera) and imaging of the upper urinary tract should be chosen on that risk and by shared decision. If a gynaecological or non-cancer cause is found, the urine test is repeated after it has resolved. The guideline was updated in 2025, and the risk categories and the place of urinary markers changed. For men with urinary symptoms and a history of blood, the EAU also suggests cystoscopy in the assessment.

On imaging, the 2023 review writes that CT urography is the most sensitive method (sensitivity 94 percent, specificity 99 percent, with low to very low certainty of evidence), ultrasound has a highly variable sensitivity (14 to 96 percent), and MR urography had a sensitivity of 83 percent. The same paper says the AUA guideline prefers kidney ultrasound for low- and intermediate-risk patients. The choice of method for you is made with your doctor on the basis of your risk, and you should not judge for yourself from these numbers.

Which signs do not wait for a visit?

If you have any of these along with blood in the urine, do not wait for an appointment; go to an emergency department now:

• You cannot pass urine, or clots have blocked the urine.
• You have fever and chills or severe flank pain.
• You have become confused or very weak.

The full list is in urgent signs. If you have only seen blood and you otherwise feel well, it is not an emergency, but the NHS says to get an urgent appointment.

A few practical suggestions

• Note the time and colour, and mention it if there were clots. A photo of the urine sometimes helps the doctor.
• List your own medicines, including blood thinners and supplements, but do not stop them.
• If an infection was treated and the blood has gone, still talk to your doctor: the AUA says to repeat the urine test after a non-cancer cause has resolved.
• For an enlarged prostate or stones, see the prostate page and the kidney stones page. Other urinary symptoms are on the page Blood in the urine, recurrent infections and leaking urine.

A reminder

This article is for general information and does not replace an examination and tests. The common causes of blood in the urine, infection, stones and an enlarged prostate, are treatable. But the only way to know the cause is to investigate.