Microscopic hematuria is the presence of red blood cells in urine, detectable only under a microscope. It is a common finding during routine medical evaluations, often without visible change in urine color. While frequently benign, it can indicate various underlying issues, including serious conditions like cancer.
What is Microscopic Hematuria
Microscopic hematuria is characterized by three or more red blood cells per high-power microscopic field in a properly collected urine sample. This differs from “gross hematuria,” where blood is visible to the naked eye, making urine appear pink, red, or tea-colored. It is typically discovered incidentally during a routine urinalysis, often when a person experiences no symptoms.
The American Urological Association defines significant microscopic hematuria as three or more red blood cells per high-power field observed in urinary sediment from at least two of three properly collected specimens. While a positive dipstick test suggests blood, a microscopic examination confirms red blood cells. Its detection warrants further investigation, though it does not automatically signify a serious problem.
Cancer Risk Associated with Microscopic Hematuria
The likelihood of detecting a genitourinary malignancy in individuals with microscopic hematuria is generally low, ranging from approximately 0.5% to 10.5%, with some studies reporting 2.6% to 5%.
Several factors increase the probability of cancer. These include age (higher risk over 35-40, especially over 60), a history of smoking, and certain chemical exposures like benzene or aromatic amines. Male sex, a prior history of gross hematuria, and irritative lower urinary tract symptoms also elevate the risk.
Common Non-Cancerous Causes of Microscopic Hematuria
Many instances of microscopic hematuria stem from benign, non-cancerous conditions. Common causes include urinary tract infections (UTIs), which often resolve with antibiotic treatment, and kidney stones that irritate the urinary tract lining.
Strenuous physical activity, especially endurance sports, can temporarily cause microscopic hematuria due to minor trauma or physiological changes. Certain medications, such as NSAIDs, blood thinners, and some antibiotics, can also contribute.
In men, benign prostatic hyperplasia (BPH) can cause microscopic hematuria. For women, menstruation may lead to a false positive or actual hematuria if the urine sample is contaminated. Other potential causes include kidney diseases, trauma, or vigorous sexual activity.
Investigating Microscopic Hematuria
When microscopic hematuria is detected, a healthcare provider typically initiates a diagnostic process to determine its cause. This often begins with a thorough medical history and physical examination, followed by a repeat urinalysis to confirm the persistent presence of red blood cells. Blood tests may also be conducted to assess kidney function.
Imaging studies are a common next step to visualize the urinary tract. Computed tomography (CT) urography is often the preferred method for evaluating the kidneys, ureters, and bladder, providing detailed images to detect stones, masses, or other abnormalities. Ultrasound may also be used, particularly in certain patient groups, but it is less sensitive for detecting small masses.
In some cases, a cystoscopy may be performed. This procedure involves inserting a thin, flexible tube with a camera into the urethra to examine the bladder and urethra directly. The specific tests ordered depend on the individual’s risk factors and the clinician’s assessment, underscoring the importance of consulting a healthcare professional for a personalized evaluation.