Red blood cells (RBCs) transport oxygen and circulate within the blood vessels. Normally, the kidneys act as highly efficient filters, preventing these cells from passing into the urine. Therefore, the presence of RBCs in a urine sample signals a disruption or breach somewhere along the urinary tract, which includes the kidneys, ureters, bladder, and urethra. This finding, known medically as hematuria, is frequently discovered during a routine urine test (urinalysis), even when no visual symptoms are present. Hematuria indicates a source of bleeding that, while often benign, always warrants attention to determine the underlying cause.
Defining Hematuria: Visible Versus Non-Visible
Hematuria is classified based on whether the blood is apparent to the naked eye. The term “gross hematuria” refers to urine that appears noticeably pink, red, or brown, resembling the color of tea or cola. This visible change suggests a larger volume of blood is present in the urine stream.
When the blood is not visible, the condition is termed “microscopic hematuria.” This finding is typically an incidental discovery made during a laboratory examination of the urine sample under a microscope. Microscopic hematuria is confirmed when three or more red blood cells per high-power field (RBCs/HPF) are counted in the urine sediment. A microscopic examination is necessary to confirm true hematuria and rule out false positives detected by a chemical dipstick test.
Common Sources of Red Blood Cells in Urine
The majority of hematuria cases are caused by conditions that are treatable or temporary. Urinary tract infections (UTIs) are frequent sources of blood, where bacteria cause inflammation and irritation in the lining of the bladder or urethra. This irritation leads to minor bleeding, and the presence of white blood cells alongside RBCs often helps confirm the infection diagnosis.
Another common source is the formation of kidney or bladder stones, which are hard masses of crystallized minerals. As these stones attempt to pass through the narrow urinary tract, they scrape against the delicate lining of the ureters or bladder. This mechanical abrasion causes trauma and subsequent bleeding, which may be accompanied by intense, radiating pain.
Strenuous physical activity, particularly endurance events like marathon running, can temporarily lead to hematuria. This phenomenon, sometimes called “march hematuria,” is believed to be caused by minor trauma to the bladder walls or increased physical stress on the kidneys. The bleeding usually resolves on its own within 24 to 72 hours after the activity ceases.
Certain medications can also increase the likelihood of finding red blood cells in the urine. Blood thinners, such as aspirin and various anticoagulants, inhibit the body’s ability to form clots, making any minor injury or irritation more likely to result in noticeable bleeding. In female patients, contamination of a urine sample with menstrual blood is a frequent, non-disease-related cause of a positive hematuria finding. Proper collection using the clean-catch method is important to minimize external contamination.
Mild, non-specific trauma to the urinary tract, such as from recent sexual activity or a minor fall, can also cause transient bleeding. Furthermore, in older males, an enlarged prostate gland, known as benign prostatic hyperplasia (BPH), can compress the urethra and cause congestion of the blood vessels around the bladder neck. This can lead to the rupture of small vessels and the release of red blood cells into the urine stream.
When Further Investigation is Necessary
Persistent or unexplained hematuria requires a thorough medical workup to rule out less common but more serious conditions. Investigation is especially necessary for patients with risk factors, such as a history of smoking, increasing age, or a family history of urinary tract issues. Diagnosis typically begins with reviewing the patient’s medical history and performing a physical examination.
Imaging the Upper Tract
The upper urinary tract (kidneys and ureters) is evaluated using medical imaging technologies. Non-invasive tests, such as a computed tomography (CT) urogram or a renal ultrasound, provide detailed images of the organs’ structure. The goal of this imaging is to detect masses, cysts, or stones, identifying structural abnormalities that could be the source of the bleeding.
Visualizing the Lower Tract
For a closer look at the lower urinary tract (bladder and urethra), a procedure called a cystoscopy may be performed. This involves inserting a thin, flexible tube with a camera into the bladder. A urologist visually inspects the lining for signs of inflammation, tumors, or ulcers.
These diagnostic steps primarily screen for serious conditions like bladder or kidney cancer, which may present initially only with hematuria. They also help identify specific types of kidney disease, such as glomerulonephritis. A full medical evaluation ensures that any potentially serious health concern is identified and treated early.