The urinary tract is made up of your bladder, your two kidneys and two ureters, and the urethra. The kidneys remove waste and excess fluid from your blood and convert it to urine. The urine then flows through two hollow tubes (ureters) — one from each kidney — to your bladder, where urine is stored until it passes out of your body through the urethra.

In hematuria, your kidneys — or other parts of your urinary tract — allow blood cells to leak into urine. A number of problems can cause this leakage, including:

• Urinary tract infections. Urinary tract infections are particularly common in women, though men also get them. They may occur when bacteria enter your body through the urethra and begin to multiply in your bladder. The infections sometimes, though not always, develop after sexual activity. Symptoms can include a persistent urge to urinate, pain and burning with urination, and extremely strong-smelling urine. For some people, especially older adults, the only sign of illness may be microscopic blood.
• Kidney infections. Kidney infections (pyelonephritis) can occur when bacteria enter your kidneys from your bloodstream or move up from your ureters to your kidney(s). Signs and symptoms are often similar to bladder infections, though kidney infections are more likely to cause fever and flank pain.
• A bladder or kidney stone. The minerals in concentrated urine sometimes precipitate out, forming crystals on the walls of your kidneys or bladder. Over time, the crystals can become small, hard stones. The stones are generally painless, and you probably won't know you have them unless they cause a blockage or are being passed. Then, there's usually no mistaking the symptoms — kidney stones, especially, can cause excruciating pain. Bladder or kidney stones can also cause both gross and microscopic bleeding.
• Enlarged prostate. The prostate gland — located just below the bladder and surrounding the top part of the urethra — often begins growing as men approach middle age. When the gland enlarges, it compresses the urethra, partially blocking urine flow. Signs and symptoms of an enlarged prostate (benign prostatic hyperplasia, or BPH) include difficulty urinating, an urgent or persistent need to urinate, and either gross or microscopic bleeding. Infection of the prostate (prostatitis) can cause the same signs and symptoms.
• Kidney disease. Microscopic urinary bleeding is a common symptom of glomerulonephritis, which causes inflammation of the kidneys' filtering system. Glomerulonephritis may be part of a systemic disease, such as diabetes, or it can occur on its own. It can be triggered by viral or strep infections, blood vessel diseases (vasculitis), and immune problems such as IgA nephropathy, which affects the small capillaries that filter blood in the kidneys (glomeruli).
• Cancer. Visible urinary bleeding may be a sign of advanced kidney, bladder or prostate cancer. Unfortunately, you may not have signs or symptoms in the early stages, when these cancers are more treatable.
• Inherited disorders. Sickle cell anemia — a chronic shortage of red blood cells — can be the cause of blood in urine, both gross and microscopic hematuria. So can Alport syndrome, which affects the filtering membranes in the glomeruli of the kidneys.
• Kidney injury. A blow or other injury to your kidneys from an accident or contact sports can cause blood in your urine that you can see.
• Medications. Common drugs that can cause visible urinary blood include aspirin, penicillin, the blood thinner heparin and the anti-cancer drug cyclophosphamide (Cytoxan).
• Strenuous exercise. It's not quite clear why exercise causes gross hematuria. It may be trauma to the bladder, dehydration or the breakdown of red blood cells that occurs with sustained aerobic exercise. Runners are most often affected, although almost any athlete can develop visible urinary bleeding after an intense workout.

The visible sign of hematuria is pink, red or cola-colored urine — the result of the presence of red blood cells. It takes very little blood to produce red urine, and the bleeding usually isn't painful. If you're also passing blood clots in your urine, that can be painful. A lot of times, though, bloody urine occurs without other signs or symptoms.

In many cases, you can have blood in your urine that's visible only under a microscope (microscopic hematuria).

To find a cause for urinary bleeding, the following tests and exams play a key role:

• Physical exam, which includes a discussion of your medical history.
• Urine tests. Even if your bleeding was first discovered through urine testing (urinalysis), you're likely to have another test to see if your urine still contains red blood cells. Hematuria that occurs just once usually doesn't need further evaluation. Urinalysis can also help determine if you have a urinary tract infection or are excreting minerals that cause kidney stones.
• Imaging tests. Most people with hematuria are likely to have an imaging test that provides detailed images of their internal organs. This might be a computerized tomography (CT) scan, which uses radiation and a powerful computer to create cross-sectional images of the inside of the body; magnetic resonance imaging (MRI), which uses a magnetic field and radio waves instead of X-rays to produce images; or an ultrasound exam. Ultrasound uses a combination of high-frequency sound waves and computer processing to view your kidneys and bladder.
• Cystoscopy. In this procedure, your doctor threads a narrow tube fitted with a miniature camera into your bladder to closely examine both the bladder and urethra.

In spite of testing, the cause of urinary bleeding may never be found. In that case, your doctor is likely to recommend regular follow-up tests, especially if you have risk factors for bladder cancer, such as smoking, exposure to environmental toxins and a history of radiation therapy.

Hematuria has no specific treatment. Instead, your doctor will focus on the underlying condition:

• Urinary tract infection. Antibiotics are the standard treatment for urinary tract infections. Symptoms usually subside a few days after you start taking medication, but recurring infections may need multiple or longer therapies.
• Kidney stones. You may be able to pass a kidney stone by drinking large amounts of water and staying active. Talk to your doctor about an appropriate amount of fluids for you. If this doesn't work, your doctor is likely to try more-invasive measures. These include a procedure that uses shock waves to break the stone into small pieces (extracorporeal shock wave lithotripsy) and, in some cases, surgery to remove the stone.
• Enlarged prostate. Treatments for an enlarged prostate seek to reduce symptoms and restore normal functioning of the urinary tract. All are effective to varying degrees, and all have some drawbacks. Medications are usually tried first, and they provide long-term relief for many men. When medications don't help, minimally invasive treatments using heat, lasers or sound waves to destroy excess prostate tissue may be tried.
• Kidney disease. Many kidney problems often require treatment. No matter what the underlying cause, the goal is to relieve inflammation and limit further damage to your kidneys.
• Cancer. Though there are a number of treatment options for kidney and bladder cancer, surgery to remove cancerous tissue is often the first choice because the cells are relatively resistant to radiation and most types of chemotherapy. The primary treatment for bladder cancer is surgical resection or complete removal of the bladder. In some cases, surgery may be combined with chemotherapy. In others, the immune system in the bladder is boosted with medications.
• Inherited disorders. Treatments for inherited disorders that affect the kidneys vary greatly. Benign familial hematuria usually doesn't require treatment, for instance, whereas people with severe Alport syndrome may eventually need dialysis — an artificial means of removing waste products from the blood when the kidneys are no longer able to do so. Sickle cell anemia is treated with medications, blood transfusions or, in the best-case scenario, a bone marrow transplant.

Although many cases of hematuria aren't serious, it's important to see your doctor any time you notice blood in your urine. Keep in mind that some medications, such as the laxative Ex-lax, and certain foods, including beets, rhubarb and berries, can cause your urine to turn red. A change in urine color caused by drugs, food or exercise usually goes away within a few days. However, you can't automatically attribute red or bloody urine to medications or exercise, so it's best to see your doctor anytime you see blood in your urine.

It's generally not possible to prevent hematuria, though there are steps you can take to reduce your risk of some of the diseases that cause it. Prevention strategies include:

• Urinary tract infections. Drinking plenty of water, urinating when you feel the urge and as soon as possible after intercourse, wiping from front to back after urination, and avoiding irritating feminine hygiene products may reduce your risk of urinary tract infections.
• Kidney stones. To help lower the likelihood of kidney stones, drink lots of water and limit salt, protein and oxalate-containing foods, such as spinach and rhubarb.
• Bladder cancer. Stopping smoking, avoiding exposure to chemicals and drinking plenty of water can cut your risk of bladder cancer.
• Kidney cancer. To help prevent kidney cancer, stop smoking, maintain a healthy weight, eat a healthy diet, stay active, and avoid exposure to toxic chemicals.