Merck Manual

Please confirm that you are not located inside the Russian Federation

honeypot link

Blood in Urine


Geetha Maddukuri

, MD, Saint Louis University

Reviewed/Revised Dec 2022
Topic Resources

Blood in the urine (hematuria) can make urine appear pink, red, or brown, depending on the amount of blood, how long it has been in the urine, and how acidic the urine is. An amount of blood too small to change color of the urine (microscopic hematuria) may be found by chemical tests or microscopic examination. Microscopic hematuria may be found when a urine test is done for another reason.

People with hematuria may have other symptoms of urinary tract disorders Overview of Urinary Tract Symptoms Kidney and urinary tract disorders can involve one or both kidneys, one or both ureters, the bladder, or the urethra, and in men, the prostate, one or both testes, or the epididymis. Problems... read more , such as pain in the side or back (flank), lower abdominal pain, an urgent need to urinate, or difficulty urinating, depending on the cause of blood in the urine. If sufficient blood is present in the urine, the blood may form a clot. The clot can completely block the flow of urine, causing sudden extreme pain and inability to urinate. Bleeding severe enough to cause such a clot is usually caused by an injury to the urinary tract.

Red urine is not always caused by red blood cells. Red or reddish brown discoloration may also result from the following:

  • Hemoglobin (which carries oxygen in red blood cells) in the urine due to the breakdown of red blood cells

  • Muscle protein (myoglobin) in urine due to the breakdown of muscle cells

  • Porphyria (a disorder caused by deficiencies of enzymes involved in the production of heme, a chemical compound that contains iron and gives blood its red color)

  • Foods (for example, beets, rhubarb, and sometimes food coloring)

  • Drugs (most commonly phenazopyridine, but sometimes cascara, diphenylhydantoin, methyldopa, rifampin, phenacetin, phenothiazines, and senna)

Causes of Blood in Urine

Blood in the urine may be caused by problems anywhere along the urinary tract from the kidneys to the ureters, bladder, or urethra. Some women at first mistake vaginal bleeding Vaginal Bleeding Abnormal vaginal bleeding includes any vaginal bleeding that occurs Before puberty Between menstrual periods During pregnancy After menopause (12 months or more after the last menstrual period) read more for blood in the urine.

Common causes

Less common causes

Less common causes include

Cancer and benign prostatic hyperplasia may cause blood in the urine. These disorders are a concern mainly in people over 50, although younger people with risk factors (smoking, family history, or chemical exposures) may develop cancer.

Disorders of the microscopic blood vessels of the kidneys (glomeruli) can be a cause at any age.

Kidney filtering disorders (glomerular disorders) may be part of a kidney disorder or may occur as a result of a disorder elsewhere in the body. These disorders are more likely if the urine has protein, clumps of red blood cells (called red blood cell casts), or malformed red blood cells. Such disorders include infections (such as a heart valve infection), connective tissue disorders (such as systemic lupus erythematosus Systemic Lupus Erythematosus (SLE) Systemic lupus erythematosus is a chronic autoimmune inflammatory connective tissue disorder that can involve joints, kidneys, skin, mucous membranes, and blood vessel walls. Problems in the... read more Systemic Lupus Erythematosus (SLE) ) and vasculitis Overview of Vasculitis Vasculitic disorders are caused by inflammation of the blood vessels (vasculitis). Vasculitis can be triggered by certain infections or drugs or can occur for unknown reasons. People may have... read more Overview of Vasculitis , blood disorders (such as serum sickness), or certain chronic disorders (such as diabetes Diabetes Mellitus (DM) Diabetes mellitus is a disorder in which the body does not produce enough or respond normally to insulin, causing blood sugar (glucose) levels to be abnormally high. Symptoms of diabetes may... read more ). Also, almost any kind of kidney damage may cause small amounts of blood in the urine.

Severe injuries, such as from a fall or a motor vehicle crash, can injure the kidneys or bladder and cause bleeding. Various procedures and surgeries (for example, inserting a catheter or doing a prostate or kidney biopsy) can also cause bleeding.

Evaluation of Blood in Urine

Doctors first try to establish that bleeding is the cause of red urine. Then they look for the cause of the bleeding, including where in the urinary tract (or occasionally elsewhere) the bleeding is originating. The following information can help people know when to see a doctor and what to expect during the evaluation.

Warning signs

In people with blood in the urine, certain symptoms and characteristics are cause for concern. They include

When to see a doctor

People who notice blood in their urine should see their doctor within a day or two. However, people who are passing a large amount of blood, who are unable to urinate, or who have severe pain should see a doctor right away.

What the doctor does

Doctors first ask questions about the person's symptoms and medical history and then do a physical examination. What they find during the history and physical examination often suggests a cause of the blood in the urine and the tests that may need to be done (see table Some Causes and Features of Blood in the Urine Some Causes and Features of Blood in the Urine Some Causes and Features of Blood in the Urine ).

Doctors ask how long blood has been present and whether there have been any previous bleeding episodes. They ask about fever, weight loss, or symptoms of urinary blockage, such as difficulty starting urination or inability to completely empty the bladder. Pain or discomfort is an important finding. Burning during urination or dull pain in the lower abdomen just above the pubic bone suggests a bladder infection. In men, mild to moderate pain in the lower back or pelvis is often the result of a prostate infection Prostatitis Prostatitis is pain and swelling, inflammation, or both of the prostate gland. The cause is sometimes a bacterial infection. Pain can occur in the area between the scrotum and anus or in the... read more . Extremely severe pain is usually due to a stone or a blood clot blocking the flow of urine.

Doctors then do a physical examination. Usually, a pelvic examination is necessary in women. If women have blood in the vagina, a catheter may need to be inserted into the bladder to see whether the source of blood is the bladder or the vagina. In men, doctors usually do a digital rectal examination to check the prostate.



Sometimes doctors can make a diagnosis based on the person's symptoms and the results of the physical examination. More often, because symptoms of many disorders overlap, testing is needed to determine the cause (or sometimes the presence) of blood in the urine. Urinalysis Urinalysis and Urine Culture Urinalysis, the testing of urine, may be necessary in the evaluation of kidney and urinary tract disorders and can also help evaluate bodywide disorders such as diabetes or liver problems. A... read more Urinalysis and Urine Culture is the first test done. Urinalysis can detect blood (confirming that the red color of the urine is caused by blood) and may show evidence of a kidney filtering disorder. If infection is suspected, urine culture is usually done.

In all people over 50 and in people who have risk factors for cancer, doctors typically use a flexible viewing tube to look inside the bladder (cystoscopy Cystoscopy A doctor can diagnose some disorders of the bladder and urethra (for example, bladder tumors, stones in the bladder, or bothersome urinary symptoms) by looking through a flexible viewing tube... read more ) to determine the cause of bleeding.

People of any age who do not have an infection or a kidney filtering disorder as the cause of visibly bloody urine typically have imaging studies, such as computed tomography (CT), ultrasonography, or magnetic resonance imaging (MRI) of the abdomen and pelvis. For people under 50 who have only microscopic hematuria and no other abnormalities detected during the physical examination, blood tests, or urinalysis, doctors may simply repeat the urinalysis in 6 or 12 months. If blood is still present, they will do further tests.

Treatment of Blood in Urine

Treatment is directed at the cause of the bleeding. Whatever the cause, if urine flow is blocked by blood clots, doctors usually insert a flexible tube in the bladder (urinary catheter) and try to flush out the blood clot.

Key Points

  • Red urine is not always caused by blood.

  • Many causes of blood in the urine are not serious.

  • Risk of serious disease increases with age and the duration of the bloody urine.

  • Testing for cancer is usually needed only for people over 50 or for younger people with risk factors for cancer.

Drugs Mentioned In This Article

Generic Name Select Brand Names
AZO Urinary Pain Relief Maximum Strength, Azo-100, Azo-Gesic, Azo-Septic, Azo-Standard, Phenazo, Prodium, Pyridium, Urinary Analgesic , Uristat, Uristat Relief, Uristat Ultra
Rifadin, Rifadin IV, Rimactane
Black Draught , Ex-Lax, Fletchers Laxative, Geri-kot, Lax-Pills, Little Remedies for Tummys, OneLAX, Perdiem, Plus PHARMA, Senexon, Senna, SennaGen , Senna-Lax , Senna-Tabs, Senna-Time, Sennatural, Senokot, Senokot Extra Strength , Senokot Xtra, SenoSol, SenoSol-X, Uni-Cenna
quiz link

Test your knowledge

Take a Quiz!