Red blood cells (RBCs) transport oxygen from the lungs to tissues throughout the body. These cells normally remain confined within the circulatory system, never entering the urinary tract. The medical term for the presence of red blood cells in the urine is hematuria, a finding that indicates a leak somewhere along the path from the kidneys to the urethra. While often temporary or benign, the discovery of blood in the urine warrants a detailed medical investigation. It signals that the kidney’s filtration barrier or the urinary tract lining has been compromised.
Identifying Red Blood Cells in Urine
The initial screening for blood in urine often begins with a chemical test using a dipstick, which reacts to the presence of hemoglobin, the protein within red blood cells. A positive dipstick result serves as a preliminary screen and must be followed by a microscopic evaluation of the urine sample for confirmation. This is necessary because the dipstick test can sometimes produce a false positive result due to the presence of other substances, such as myoglobin from severe muscle breakdown.
The definitive diagnosis of hematuria relies on microscopic analysis of the spun-down urine sediment. Healthcare providers generally define microscopic hematuria as the finding of three or more red blood cells per high-power field (HPF) under the microscope. This standard threshold ensures that the number of cells counted is truly abnormal, as a very small number of red blood cells can sometimes be found in a normal urine specimen.
Understanding the Types of Hematuria
Hematuria is typically categorized into two types based on the visibility of the blood in the urine. Microscopic hematuria occurs when the amount of blood is so small that it can only be detected through laboratory testing, often during a routine urinalysis. In these cases, the patient’s urine appears normal in color, and they are frequently unaware of the condition.
The other type, known as gross hematuria, is characterized by visible changes in the urine color, which may appear pink, red, or even a dark, tea-like brown. Gross hematuria results from a much larger volume of blood loss into the urinary tract. Clinically, the presence of gross hematuria is considered more significant because it carries a substantially higher risk of being associated with a serious underlying disorder, such as cancer, compared to microscopic hematuria.
Primary Causes of RBC Presence
The source of red blood cells in the urine can originate from anywhere in the urinary system, from the kidneys down to the urethra. Many instances are transient and resolve on their own, such as after strenuous exercise. Temporary irritation from recent sexual activity or menstrual contamination can also lead to a temporary finding of red blood cells. Certain medications, including blood thinners, can also increase the likelihood of bleeding into the urinary tract.
Common urological causes often involve inflammation or physical disruption of the urinary tract lining. Urinary tract infections (UTIs) are a frequent cause, where bacteria irritate the lining of the bladder or urethra, causing the small blood vessels to leak. Similarly, the passage of a kidney stone can scrape against the delicate tissue of the ureter as it moves, resulting in bleeding that ranges from microscopic to visible. In older men, an enlarged prostate gland can press on the urethra, leading to irritation and the presence of red blood cells.
More serious conditions that cause hematuria involve damage to the kidneys’ filtering units or the development of abnormal growths. Glomerulonephritis is a type of kidney disease where the glomeruli, the tiny filters within the kidney, become inflamed and allow red blood cells to leak into the urine. This is often suggested by the presence of misshapen red blood cells or protein in the urine, indicating a kidney origin. Cancers of the bladder or kidney can cause bleeding when tumors erode into the urinary tract lining, necessitating thorough investigation, especially in cases of gross hematuria.
Next Steps Following a Positive Result
Following the confirmation of hematuria, the next steps involve a targeted diagnostic pathway to determine the source and seriousness of the bleeding. The evaluation is often risk-stratified, meaning the extent of testing depends on the amount of blood, the patient’s age, and other risk factors like a history of smoking. Initial steps typically involve a repeat urinalysis to confirm the persistence of hematuria and a urine culture to rule out an underlying infection.
Further investigation often includes blood tests to check kidney function, such as measuring creatinine and estimated glomerular filtration rate (eGFR). Imaging studies are commonly performed to visualize the urinary tract and look for stones or masses. An ultrasound is often the first imaging choice, but a computed tomography (CT) urogram may be used, as it provides detailed images of the kidneys, ureters, and bladder. For high-risk patients, a urologist may perform a cystoscopy, where a small camera is inserted into the bladder to directly examine its lining for any abnormalities.