It could be cancer, kidney stones, urinary tract infection, or even a false positive lab test. Your primary care physician can handle many cases of blood in the urine. In some cases you'll need to see a urologist for an evaluation. In other cases, doctors at the Cleveland Clinic recommend that you see a nephrologist.
Blood in the urine may be obviously visible. This is called gross or macroscopic hematuria, and calls for an evaluation by a urologist in most cases. It may be just a urinary tract infection that can be treated easily with antibiotics, or it may be cancer somewhere in the urinary system. Urologic cancers typically produce intermittent bleeding, so doctors caution against this scenario: Patient goes to primary care physician with bladder pain and blood in the urine. Physician diagnoses urinary tract infection and prescribes antibiotics. The pain and bleeding clear up; both patient and doctor consider the treatment successful. But the patient actually has cancer, which continues to grow until symptoms return. To prevent this mistake, the authors of Reference 1 recommend always doing a urine culture before prescribing an antibiotic for patients with blood in the urine.
At the other end of the risk spectrum, these authors encourage primary care physicians not to refer patients to a urologist if the only sign of blood in the urine is a positive dipstick test. Microhematuria means small amounts of blood in the urine, visible only with microscopic examination of a properly prepared urine specimen. The dipstick test is a simple, low-cost test for microhematuria. Unfortunately, this test is not very accurate. Up to 75% of the patients referred to their urology clinic with microhematuria are found to have nothing wrong. To prevent this mistake, Dr. Rao and Dr. Jones recommend doing the slightly more expensive microscopy test for blood in the urine before sending the patient to a urologist. A Medicare level-4 urological consultation for hematuria costs $170, and exposes the patient to invasive procedures that have their own health risks.
An evaluation by a nephrologist is appropriate if the patient has these lab results: