Blood in urine (hematuria) may not always be a cause for worry.

It’s almost a natural response – when we see blood, we think something must be wrong. However, blood in urine, termed hematuria by doctors, isn’t always a cause for concern.

“Blood in urine is one of the most common issues affecting both younger and older patients seen in the urology clinic,” says Dr Nor A​​zhari Bin Mohd Zam, Consultant, Department of Urology, Singapore General Hospital (SGH), a member of the SingHealth group.

“In the young, the most common causes are urinary stones or a urinary tract infection (UTI). In older patients, it is more likely to be bladder or kidney cancer, especially if the blood in the urine is painless and the patient has a history of smoking,” he adds.

When blood in urine is not serious

Certain medications including aspirin, heparin or warfarin (a blood thinner) and anti-cancer drug cyclophosphamide have been known to cause blood in urine.

Sometimes, it’s just tiny traces that can only be seen under a microscope. This is called microscopic hematuria. Blood which is visible to the naked eye is termed gross hematuria. The chance of finding a significant urological disease is much higher in patients with gross, rather than microscopic, hematuria.

Apart from medicine, certain foods such as beets, rhubarb and berries, consumed in large quantities, can also cause your urine to turn reddish for up to a few days. Even strenuous exercise can bring about gross hematuria, though it’s unclear why.

It is always best to see a doctor upon discovering blood in your urine, so more serious causes can be ruled out.

When blood in urine could be serious

Conditions affecting the kidney, ureter, bladder or prostate can lead to blood in urine.


Hematuria may be caused by kidney inflammation (a condition known as glomerulonephritis) or by a kidney infection, especially when associated with fever and loin pain.

Another possible cause is a kidney stone, but perhaps the most severe cause is kidney cancer. In kidney cancer, there can be a lot of blood and clots in the urine, but it is usually painless.

Ureter and bladder

When the blood in urine originates from the ureter, a likely cause is a urinary stone. The patient will usually have accompanying pain in the loin. A tumour in the ureter, although uncommon, is usually malignant and generally causes painless hematuria.

However, if blood in urine is accompanied by painful urination, urinary frequency and possibly fever, then it could be due to a UTI. UTIs are treated by oral antibiotics or, in more serious cases, by intravenous antibiotics.

A bladder stone is another common cause for hematuria. However, if the patient is a male smoker, aged 50 and above, who experiences painless blood in his urine, there is a chance he could be suffering from bladder cancer.


Hematuria resulting from a bleeding prostate could be a sign of either a prostate infection, a benign enlargement of the prostate or prostate cancer. Typically, patients with a prostate condition encounter difficulty in urinating or frequent urination, as well as poor urinary flow.

Tips to prevent hematuria

Blood in urine may be difficult to prevent but here are some steps you can take to reduce your risk.
  • If you have kidney stones: Drink sufficient fluids, monitor your salt intake and reduce your intake of foods rich in oxalates and animal protein.
  • If you have gout: Reduce your intake of foods rich in purine to keep your uric acid in check.
  • If you’re a smoker: To minimise your risk of kidney or bladder cancer, the most effective way is to avoid smoking. “The risk of having bladder cancer is 4-5 times higher in smokers than non-smokers. In addition, smokers are twice as likely to develop kidney cancer,” explains Dr Nor Azhari.

Ref: S13