Occult blood is when you can’t see blood in your urine with your eye and it’s only visible under a microscope. You may need antibiotics or different treatments depending on the infection or other causes.

Being told you have blood in your urine can be concerning, especially if you cannot see the blood.

In medicine, the word “occult” means “hidden.” Occult blood in the urine means the blood in the urine is only visible under a microscope.

Here’s what you need to know about this test result, what conditions may cause it, and what additional testing you may encounter.

The medical term for blood in the urine is hematuria.

Blood in the urine may be tinged pink or red. When you can see it, this is considered gross hematuria.

When blood is in the urine but you cannot see any pink, red, or clotting, it’s considered occult blood. Another name for this condition is microscopic hematuria.

Doctors typically divide microscopic hematuria into categories depending on how much blood is found in the urine under the microscope (microscopy).

  • Significant microscopic hematuria: 3 or more red blood cells (RBC)/hpf (≥ 3 RBC/hpf)
  • Insignificant microscopic hematuria: 2 or fewer RBC/hpf (0-2 RBC/hpf)

Significant microscopic hematuria warrants further testing.

Readings in the insignificant category do not necessitate further testing unless symptoms or other issues develop.

There are numerous reasons you may have blood in your urine. Some involve health conditions, like infection or cancer, and others relate to certain activities or even trauma.

Causes include:

Blood in the urine may also be caused by more serious issues:

Dehydration may also lead to blood in the urine.

When this happens, it’s considered a false positive result because it does not relate to disease. Other causes of false positives in a urine dipstick test (a type of urinalysis) include:

  • hard exercise
  • the presence of menstrual blood in the sample
  • recent sexual activity
  • free hemoglobin or myoglobin

Doctors and labs use a few different tests to look for blood in the urine.

Urinalysis (microscopic exam) is usually the first test you’ll encounter after a dipstick test. In this test, you’ll be asked to urinate in a cup. You’ll need to do a “clean catch” and follow the instructions closely to ensure your sample isn’t contaminated. The lab will then look closely at the sample under a microscope.

Additional testing may include:

What if you get a false positive or negative test result?

False positive test results for occult blood in the urine are relatively common (22%) with dipstick testing.

To be a true false positive, a microscopy test must also be negative. False negatives are less common (4%).

Diet, exercise, medications, and hydration may all affect test results. If you have concerns about your results, ask your doctor if a re-test may be warranted.

The treatment for blood in the urine depends on the underlying cause.

For example:

  • infection may be treated with antibiotics
  • dehydration may be treated by giving fluids
  • enlarged prostate may be treated with medication
  • bladder or kidney stones may be treated with sound waves (lithotripsy)

In cases where the blood is caused by benign things — like exercise or menstrual blood — no treatment may be necessary.

You may have blood in your urine even if you cannot see it. If your doctor tests your urine and the test comes back positive for hematuria, you may or may not need further testing.

The next steps hinge on how much blood was found in the urine and what other symptoms you’re experiencing.