The presence of red blood cells (RBCs) in the urine is known as hematuria, indicating that blood cells have entered the urinary tract. The urinary system (kidneys, ureters, bladder, and urethra) filters waste and is designed to prevent blood cells from passing through. The appearance of RBCs suggests a breach or irritation along this pathway. Hematuria is categorized by visibility: gross hematuria appears pink, red, or tea-colored, while microscopic hematuria is invisible and only detectable through laboratory testing, often discovered incidentally during routine screening.
Detecting Red Blood Cells in Urine
The initial step in detecting hematuria is typically a urinalysis, often starting with a urine dipstick test. This test uses a chemically treated strip that changes color when it detects hemoglobin. While convenient, the dipstick test is highly sensitive and can sometimes produce a false-positive result, reacting to substances other than whole red blood cells, such as myoglobin from severe muscle breakdown. For a definitive diagnosis, a positive dipstick result must be confirmed by a microscopic examination of the urine sediment. Microscopic hematuria is confirmed when three or more red blood cells are observed per high-power field (HPF) in a centrifuged urine sample. Proper collection of a midstream, “clean-catch” sample is important to prevent contamination from external sources, such as menstrual blood or hemorrhoids.
Common and Temporary Reasons for Hematuria
Many instances of hematuria are temporary and caused by conditions that irritate the urinary tract lining. Urinary tract infections (UTIs) are a frequent cause, where bacteria colonize the urethra, bladder, or kidneys, leading to inflammation that causes superficial bleeding. This inflammation disrupts the mucosal lining, allowing red blood cells to leak into the urine. The presence of white blood cells and bacteria in the urinalysis usually confirms an infection as the source.
Strenuous physical activity, particularly long-distance running, is a recognized cause of transient hematuria, sometimes called “march hematuria.” This phenomenon is thought to be caused by direct trauma to the bladder walls from repeated impact or by temporary changes in blood flow to the kidneys during intense exercise. The hematuria caused by this mechanism usually resolves on its own within 24 to 72 hours after the activity ceases.
The passage of small kidney stones can also cause bleeding, as the sharp, crystalline edges of the stones scrape against the lining of the ureter or bladder. Certain medications, including common blood thinners like warfarin and some non-steroidal anti-inflammatory drugs (NSAIDs), can also increase the likelihood of bleeding by interfering with the blood clotting process. Dehydration and recent sexual activity can cause minor irritation to the urethra, which may also result in a small, self-limiting amount of blood in the urine.
Serious Underlying Medical Conditions
While many causes are temporary, hematuria can occasionally signal a more serious underlying health issue that requires prompt investigation. Conditions affecting the kidney’s filtering units, the glomeruli, are a significant concern and are collectively known as glomerulonephritis. In these diseases, the fine, porous structure of the glomerular basement membrane becomes damaged, allowing red blood cells to pass into the urine filtrate.
Red blood cells that have passed through a damaged glomerulus often appear distorted and fragmented, known as dysmorphic RBCs. Other forms of kidney disease, such as polycystic kidney disease, can also lead to bleeding due to the rupture of fluid-filled cysts within the kidney tissue. Bleeding originating from the kidney’s filtering apparatus often involves additional findings, such as protein in the urine, which suggests a deeper issue with kidney function.
Cancers of the urinary tract, particularly bladder, kidney, and prostate cancer, must be ruled out, especially in older individuals and smokers. Bladder tumors are often fragile and bleed intermittently into the urine, which may be the sole symptom in the early stages of the disease. In men, an enlarged prostate gland, or benign prostatic hyperplasia (BPH), can cause hematuria as the swollen gland compresses the urethra and causes distension of the small blood vessels. Significant trauma to the abdominal or flank area can also damage the urinary system, resulting in gross hematuria usually accompanied by pain and other symptoms.
Diagnostic Follow-up and Treatment Principles
Once hematuria is confirmed, the medical focus shifts to the differential diagnosis—the process of systematically narrowing down the potential causes. The physician will consider the patient’s age, medical history, and risk factors, such as smoking, to determine the necessary follow-up tests. The initial urinalysis often guides the next steps, with the presence of dysmorphic red blood cells or protein pointing toward a kidney (nephrology) specialist.
Advanced imaging studies are typically employed to visualize the entire urinary tract, including the kidneys, ureters, and bladder. A computed tomography (CT) urogram or renal ultrasound can detect kidney stones, tumors, or structural abnormalities like cysts. For direct visualization of the bladder lining, a procedure called cystoscopy involves inserting a thin, lighted tube with a camera through the urethra. This allows a urologist to inspect the bladder for sources of bleeding, such as tumors or inflamed areas.
Treatment for hematuria is not directed at the blood in the urine itself, but rather at the specific underlying cause identified through the diagnostic process.
Treatment Examples
For a UTI, treatment involves a course of antibiotics to clear the infection and resolve the inflammation.
In cases of kidney stone irritation, management focuses on pain control and facilitating the stone’s passage, or removal if necessary.
If a serious condition like cancer or a specific form of kidney disease is diagnosed, the patient will be referred to the appropriate specialist for a targeted treatment plan.