I am 27 years old and in good health. At a routine gynecological exam, blood was found in my urine. A week later, with increased water intake, they again found blood in my urine. Though a nurse practitioner said there was no sign of infection, she put me on antibiotics and told me to return in 10 days. Why am I being treated for an infection when one isn't present? Why might I have blood in my urine?

--Suzanne

Many conditions can cause hematuria, or blood in the urine. Bladder and kidney infections are frequent causes; sometimes an infection won't show up in an office test but will appear in a urine culture, a test that takes longer to run. Kidney stones are another possibility; you might need a test called an intravenous pyelogram (IVP), in which dye is injected into a vein and a series of X-rays trace its path through your kidneys and urinary tract. Sometimes a urologist (specialist in the urinary tract) needs to look directly into the bladder with a telescope-like instrument, a procedure called cystoscopy.

Some other medical conditions can also cause blood in the urine. Diseases like sickle-cell anemia, lupus or nephropathy (kidney disease) are possibilities. And don't forget the most common reason for blood in the urine in women -- menstruation!

Sometimes the test result is a "false positive," meaning the reading is an error and there really is no blood. For instance, sometimes the antiseptic you use to cleanse yourself for a clean-catch urine specimen can cause a false-positive reaction on a urine dipstick test for blood. Or if you've had a recent muscle injury (or engage in very strenuous exercise), then substances released from the injured muscle can cause a false positive.

If your hematuria persists, and your doctor finds no easy explanation, you should follow up with a urologist.