The presence of red blood cells (RBCs) in a urine sample, often discovered during a routine urinalysis, can be a confusing finding for many patients. Red blood cells are typically responsible for carrying oxygen throughout the body, and their appearance in the urine indicates a breach somewhere along the urinary tract. The urinary system, which includes the kidneys, ureters, bladder, and urethra, is designed to prevent these cells from passing into the final waste product. This finding signals that a medical evaluation is warranted to determine the origin of the leakage.
Defining Hematuria
The medical term for the presence of red blood cells in the urine is hematuria. Clinicians categorize this finding into two main types based on visibility. Gross hematuria (macroscopic) describes blood visible to the naked eye, often turning the urine pink, red, or tea-colored brown. Microscopic hematuria involves an amount of blood too small to be seen without laboratory magnification and is usually discovered incidentally during routine urinalysis. To be classified as true microscopic hematuria, a standard threshold of three or more red blood cells per high-power microscopic field (\(\ge 3\) RBC/HPF) must be observed in the urine sediment.
Common Sources of Red Blood Cells in Urine
The source of red blood cells can originate from any point in the urinary system, from the kidney’s filtering units down to the urethra. While some causes are temporary and benign, others signal the need for a comprehensive investigation. Sources are generally categorized into transient causes and conditions involving the urinary tract structure or function.
Temporary and Non-Urinary Sources
A common transient cause is strenuous physical activity, often seen in long-distance runners, sometimes termed “jogger’s hematuria.” This temporary bleeding is thought to be caused by physical trauma to the bladder lining or increased blood flow during intense exercise. Certain medications can also lead to hematuria, including antibiotics like penicillin, pain relievers like nonsteroidal anti-inflammatory drugs (NSAIDs), and anticoagulant therapy. Anticoagulants do not cause the bleeding itself but can exacerbate blood loss from an existing lesion that would otherwise go unnoticed.
Urinary Tract and Structural Issues
Infections are a frequent cause, as a urinary tract infection (UTI) or a kidney infection (pyelonephritis) causes inflammation and irritation of the lining of the urinary passages. Kidney or bladder stones (nephrolithiasis) are a common structural cause, where the rough edges of the mineral deposits scrape against the delicate lining of the urinary tract as they pass. In men over 50, an enlarged prostate gland, known as Benign Prostatic Hyperplasia (BPH), can also cause bleeding by compressing the urethra.
Glomerular and Malignant Conditions
More serious origins include conditions that directly affect the kidneys’ filtering units, the glomeruli. Glomerular bleeding is characterized by the presence of protein in the urine and red blood cells that appear dysmorphic (misshapen) from being squeezed through a damaged filter. These conditions, such as various forms of glomerulonephritis, typically require evaluation by a kidney specialist. Hematuria can also be the first or only sign of malignancy, such as bladder, kidney, or prostate cancer, especially in patients with associated risk factors.
Diagnostic Procedures for Pinpointing the Cause
Once hematuria is confirmed, healthcare providers initiate a structured investigative process to determine the exact source. The first step involves a repeat urinalysis and blood tests to assess kidney function, such as measuring serum creatinine and estimated Glomerular Filtration Rate (eGFR). The presence of other findings, like high levels of protein or dysmorphic red blood cells, can suggest a kidney-related (nephrological) issue.
The subsequent workup is guided by a risk stratification model considering factors like patient age, smoking history, and the severity of the bleeding. Patients categorized as high-risk, such as those over 60 with a history of heavy smoking or gross hematuria, require a comprehensive evaluation to rule out cancer. This evaluation includes specialized imaging of the upper urinary tract, typically a CT urogram, and a visual inspection of the bladder.
Lower-risk patients may initially undergo a less invasive renal ultrasound and a repeat urinalysis after a period of observation. A procedure called cystoscopy, where a thin, lighted camera is inserted into the urethra to examine the bladder lining, is often reserved for intermediate or high-risk patients. This structured approach aims to identify the underlying cause while minimizing unnecessary invasive tests for those at low risk of serious disease.