Guide to Occult Blood

WRITTEN BY

The Levels Team

Updated: 05/22/2025|12 min read

Summary

Occult blood in urine means that there is blood in the urine that's not visible to the naked eye but can be detected through laboratory tests.

Why It Matters

Occult blood in urine, called microscopic hematuria, is a common finding and can be a sign of a range of conditions. "Occult" means hidden or concealed. Under normal circumstances, the kidneys filter blood to remove waste products and excess water, creating urine that should be free of blood cells. When blood cells appear in urine, it's a sign that there's a problem somewhere in the urinary tract, which includes the kidneys, ureters, bladder, and urethra.

In the kidneys, damaged glomeruli (the kidneys' filtering units) may allow red blood cells to pass into the urine. Or the lining of the ureters, which transport urine from the kidneys to the bladder, can become irritated or damaged, causing microscopic bleeding. Similarly, inflammation or injury to the bladder lining or urethra can cause blood cells in urine.

Kidney stones can physically scrape against tissue, creating microscopic injury, and infections can cause inflammation that triggers some microscopic bleeding.

A single elevated urinalysis result may not be cause for concern, especially if it occurs after intense physical activity or during menstruation in women. Your healthcare provider will order other tests to diagnose the cause of the occult blood in your urine.

Associated Symptoms

Occult blood in urine itself is a laboratory finding rather than a medical condition. However, its presence may be associated with various urinary tract issues, each with its own symptoms.

Common symptoms that may indicate conditions associated with occult blood in urine:

• Painful urination: Burning or discomfort during urination may indicate a urinary tract infection or inflammation
• Frequent urination: Increased urge to urinate can be associated with UTIs, bladder irritation, or prostate issues
• Lower abdominal pain: Discomfort in the pelvic region may be related to bladder inflammation or infection
• Flank pain: Pain in the side or back below the ribs may suggest kidney stones or kidney infection
• Fatigue: Persistent tiredness that may occur with kidney disease or chronic disease, which may cause blood in urine
• Fever and chills: Temperature elevation can suggest infection, particularly UTI or pyelonephritis (kidney infection)

It's important to note that many conditions causing occult blood in urine can be asymptomatic. For example, early kidney disease, some bladder tumors, and even some kidney stones may not cause noticeable symptoms despite causing microscopic bleeding. Discuss with your physician if routine urinalysis can be valuable for early detection of problems before symptoms develop.

Clinical Ranges

Lab Reference Range: Negative

Lifestyle Factors That Can Impact It

Activities that may affect occult blood in urine include:

• Intense exercise: Very strenuous exercise, particularly long-distance running or high-impact activities, can cause microscopic trauma to the bladder or kidneys, leading to temporary blood in urine. This is known as exercise-induced hematuria and typically goes away with rest.

Other habits can increase the risk of urinary tract infections, such as:

• Personal hygiene: Poor hygiene practices can introduce bacteria to the urinary tract. Proper wiping technique (front to back), regular cleaning, and wearing breathable underwear can help prevent bacterial growth.
• Sexual activity: Frequent sexual activity can increase the risk of UTIs, especially in women. Urinating before and after sexual activity can help reduce bacterial transfer.

Other Factors That Can Impact It

Genetic Conditions

• Sickle cell disease: An inherited condition where red blood cells become crescent-shaped and break down easily, which can lead to blood in urine.
• Alport syndrome: A genetic disorder affecting kidney filters, causing progressive kidney damage and blood in urine.
• Polycystic kidney disease: An inherited condition causing fluid-filled cysts to grow in the kidneys, which can rupture and cause bleeding.

Medical Conditions

• Urinary tract infections (UTIs). UTIs are one of the most common causes of elevated RBCs in urine. The infection causes inflammation of the urinary tract lining, leading to increased red blood cells.
• Kidney stones. These are mineral deposits that can develop in the kidneys. They can scrape and damage the urinary tract as they move, causing bleeding.
• Glomerulonephritis. This kidney condition involves inflammation of the filtering units (glomeruli), allowing RBCs to leak into urine.
• Bladder or kidney cancer. While less common, these conditions can cause persistent hematuria.
• Enlarged prostate. In men, an enlarged prostate can cause increased RBCs due to pressure on the urethra and bladder, potentially leading to inflammation and bleeding.

Medications and Supplements

• Blood thinners
• Aspirin and nonsteroidal anti-inflammatory drugs (NSAIDs), though research is mixed
• Certain antibiotics
• Some herbal supplements

Individual Factors

• Age: Older adults are more susceptible to conditions causing blood in urine, such as enlarged prostate or cancers
• Gender: Men are more prone to kidney stones, while women are more prone to UTIs
• Pregnancy: The increased pressure on the urinary system can cause temporary bleeding
• Menstruation: Can contaminate urine samples with blood

Testing Accuracy and Stability

Occult blood testing is generally reliable, but certain factors may impact results.

Factors That Can Affect the Accuracy of Your Test

• Menstrual blood contamination
• Recent sexual activity
• Excessive exercise just before testing

How It Relates to Other Markers

Other tests can provide insights about health status when they're viewed alongside occult blood results. These tests may include:

• Protein in urine (Proteinuria). May appear alongside occult blood in conditions affecting kidney function. The presence of both markers can indicate more significant kidney involvement.
• White blood cells (WBCs). Elevated WBCs may indicate infection or inflammation.
• Nitrites and leukocyte esterase. These markers help confirm or rule out urinary tract infections when occult blood is present.
• Creatinine to check kidney function
• Other urinary findings, in addition to protein: presence of crystals
• Hemoglobin to determine if there is anemia

What Results May Mean in the Context of Other Markers

• Occult blood + protein in urine + abnormal kidney function tests: This combination can indicate glomerular disease, where the kidney's filtering units are damaged.
• Occult blood + nitrites in urine + white blood cells in urine: This can indicate a urinary tract infection.
• Occult blood + normal urine culture + normal kidney function: When blood appears without signs of infection or kidney dysfunction, other causes like stones or tumors may be possible.

Follow-up Considerations

If you have occult blood in your urine, your provider may make some of the following recommendations. You should always speak to your doctor if you have medical questions or before making medical decisions.

When Re-Testing May Be Appropriate

• After initial abnormal results (within 2-4 weeks)
• Following completion of treatment
• Regularly if monitoring a chronic condition

Additional Testing Your Doctor May Consider

• 24-hour urine collection
• Imaging tests of the kidneys
• Urine cytology to check for cancer cells
• Serum PSA for men to evaluate prostate issues
• Blood tests for autoimmune markers if glomerulonephritis is suspected
• Kidney function tests: BUN, creatinine
• Straining the urine to identify the stone type in people where a kidney stone is identified

When Additional Care May Be Warranted

• If occult blood in urine persists after initial treatment
• Visible blood in urine
• Symptoms like flank pain, fever, or significant urinary symptoms that don't resolve
• Occult blood with declining kidney function test results
• Family history of kidney disease or urological cancer

Bibliography