Microscopic hematuria is a common condition. Most of its causes are benign. However, it may be a warning of something more ominous in some patients.

Gross blood in the urine or visible hematuria, especially with blood clots, needs urgent attention. Although the cause may be something simple like infection, it is important to diagnose more serious causes such as cancer and stone disease.

Possible causes of blood in the urine range from minor, incidental findings that do not require treatment to highly significant lesions that may be a threat to the patient’s wellbeing and life.

• Urinary tract infections.
  Urinary tract infections are particularly common in women, though men also get them. Associated symptoms can include frequent urge to urinate, pain and burning with urination, and strong-smelling urine.
  
  Kidney infections (pyelonephritis) can occur when bacteria enter the kidneys from the bloodstream or move from up from the bladder to the kidney. 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 turn into small, hard stones. The stones are generally painless, unless they cause a blockage or are being passed. Kidney stones can cause excruciating pain. They can also cause both gross and microscopic bleeding.
  
  
• Enlarged prostate.
  This is one of the leading causes of visible blood in the urine in men older than 50. The prostate gland located just below the bladder, and surrounding the urethra, often begins growing as men approach middle age. When the gland enlarges, it compresses the urethra, partially blocking urine flow. Symptoms of an enlarged prostate (benign prostatic hypertrophy or BPH) include difficulty urinating, an urgent or persistent need to urinate, and either gross or microscopic bleeding. Please read more in the Prostate Clinic section. Infection of the prostate (prostatitis) can cause the same signs and symptoms.
  
  
• Kidney disease/ kidney inflammation (Glomerulonephritis)
  Microscopic urinary bleeding is a common symptom of inflammation of the kidneys known as glomerulonephritis. Glomerulonephritis may be part of the effect of diseases such as diabetes, or it can occur on its own. Viral or bacterial infections, blood vessel inflammation (vasculitis), and immune diseases such as IgA nephropathy, which affects the small capillaries that filter blood in the kidneys (glomeruli), can trigger it.
  
  
• Cancer.
  Visible urinary bleeding may be the first sign of kidney cancer, bladder cancer, ureteric cancer or prostate cancer. In the early stages, there may not be any pain in the affected organs.
  
  
• Inherited disorders.
  Sickle cell anemia and Alport Syndrome are examples of inherited disorders that can cause blood in urine, both gross and microscopic hematuria. 
  
  
• Kidney injury.
  A blow or a knock on the kidneys from an accident or contact sports can cause gross blood in the urine. The force is usually fairly great to cause blood in the urine, especially gross hematuria. If the force is slight but there is gross hematuria, there may be an abnormality in the kidneys such as an obstructed kidney.
  
  
• Medications.
  Common drugs that can cause visible urinary blood include aspirin, penicillin, blood thinners such as warfarin and heparin, and the anti-cancer drug cyclophosphamide (Cytoxan).
  
  
• Strenuous exercise.
  This is likely due to dehydration. Breakdown of red blood cells very rarely occurs with sustained aerobic exercise. Any athlete can develop visible urinary bleeding after an intense workout.