In healthy men and women, urine does not contain any blood that can be seen with the eye, called "gross blood," nor does it contain red blood cells that can be discovered with the aid of a microscope. The discovery of either gross or microscopic blood in urine is a sure indication of the need to examine and evaluate the patient to discover the cause of this abnormality. The conditions that can lead to either gross or microscopic blood in the urine are many and varied.
In adults, a careful history to describe the details of the bloody urine, a physical examination and laboratory studies are the first step in unearthing the cause. Imaging with x-rays, ultrasound, CAT/MRI scans are the next step and will usually discover the cause. In adult women, infection of the bladder or kidneys, urinary stones, and tumors of the urinary bladder, kidneys are the most common causes. In adult men, enlargement and/or infection of the prostate, bladder infection and tumors (usually malignant) of the bladder, kidneys, or ureters are the three most common reasons for blood in the urine.
Infections in both men and women are treated with appropriate antibiotics and some patients must be placed on preventative antibiotics over a long period of time to keep them infection free. Urinary stones can occur either in the kidneys, bladder or in the ureters (tubes that connect the kidneys to the bladder). Some urinary stones will pass on their own, some will require fragmentation into smaller stones by a machine called a lithotripter, with the smaller fragments being allowed to pass out or be removed by an urologist with an instrument.
In older men, enlargement of the prostate can cause bloody urine and other symptoms, and can be treated by medication in many cases and by surgical removal by an instrument by urologist in those patients not responding to the medications. The important message of this discussion on blood in the urine is very simple and most important. NEVER IGNORE BLOOD IN THE URINE even if it only occurs once!
In children, the most common reasons for blood in urine are congenital abnormalities of the urinary tract and infections. Obtaining imaging of the urinary tract with x-rays or ultrasound as well as cultures to confirm infection will usually produce the correct diagnosis. A course of antibiotics will usually cure the urinary infection; congenital abnormalities often need surgery for correction.