Temporary or Benign Blood in Urine

Visible vs microscopic blood

• Gross (visible) hematuria: urine looks pink, red, cola-colored or contains clots. Even a small amount of blood can change the color.
• Microscopic hematuria: blood is found only with a dipstick or under a microscope. The American Urological Association defines significant microhematuria as 3 or more red blood cells per high-power field on a properly collected sample.

A dipstick alone can be positive for other reasons, so a microscopic urine exam is needed to confirm red blood cells.

Benign and temporary causes

Exercise

Hard or long exercise, especially long-distance running, can cause blood in the urine. Causes include bladder wall bumping during running, reduced kidney blood flow and dehydration. It usually clears within 24 to 72 hours. Persistent or recurrent blood after exercise still needs evaluation.

Menstruation and contamination

Blood from menstruation, vaginal bleeding or hemorrhoids can contaminate a urine sample. Doctors usually repeat the test when you are not on your period, using a clean-catch sample.

Urinary tract infection

A urinary tract infection inflames the bladder lining and commonly causes blood, along with burning, urgency and frequency. After treatment, a repeat urine test should show that the blood has cleared.

Sexual activity and minor trauma

Vigorous sex, a recent catheter, or a minor blow can cause brief bleeding.

Kidney stones

Passing a kidney stone often causes visible or microscopic blood with severe flank pain. Blood typically clears after the stone passes.

Benign kidney conditions

• thin basement membrane disease: an inherited, usually harmless kidney filter variant causing persistent microscopic blood, often in families
• sickle cell trait: can cause episodes of painless blood in the urine
• enlarged prostate (benign prostatic hyperplasia): fragile blood vessels can bleed

Medicines

Blood thinners do not usually cause hematuria on their own but can unmask an underlying cause, so bleeding on blood thinners should still be investigated.

Red urine without blood (pseudohematuria)

When blood in urine is not benign

Doctors investigate further when blood:

• is visible, even once
• persists on repeat testing
• occurs with protein in the urine, high blood pressure or abnormal kidney function

Concerning causes include:

• bladder cancer, the most important cause in older adults and smokers
• kidney cancer
• prostate cancer
• glomerulonephritis and other kidney diseases
• polycystic kidney disease

Risk factors for cancer include age over 35 to 40, smoking (current or past), male sex, exposure to certain chemicals and dyes, previous pelvic radiation and visible blood.

How doctors assess it

1. repeat urinalysis with microscopy to confirm red blood cells
2. check for infection with a urine culture, then retest after treatment
3. kidney function and blood pressure, and urine protein
4. risk assessment based on age, sex, smoking history and number of red cells
5. depending on risk: - repeat urine test in 6 to 12 months for low-risk people - imaging with kidney ultrasound or CT urography - cystoscopy, a camera look inside the bladder, for intermediate and high-risk people and anyone with visible blood

Kidney disease features, such as protein in the urine, abnormally shaped red cells or rising creatinine, lead to referral to a nephrologist.

Frequently asked questions

Can blood in urine be harmless?

Yes. Hard exercise, menstrual contamination, urinary infections, recent sex, minor injury and passing a kidney stone can cause temporary blood in the urine. But it should never be assumed harmless until a doctor confirms it with a repeat test and, if needed, further assessment.

How long does blood in urine last after exercise?

Exercise-induced blood in the urine usually clears within 24 to 72 hours. If it lasts longer, keeps coming back, or you notice dark cola-colored urine with muscle pain, see a doctor.

Should I worry about microscopic blood in my urine?

Microscopic blood is common and often not serious, but it needs follow-up. Your doctor will repeat the test, check for infection and assess your risk. Older adults, smokers and people with persistent blood usually need imaging and a bladder exam.

What foods can make urine look red?

Beets, blackberries, rhubarb and foods with red dyes can tint urine pink or red without any blood. Some medicines, like rifampin and phenazopyridine, also change urine color. A urine test can confirm whether blood is present.