Hematuria refers to the presence of blood in the urine. Asymptomatic microscopic hematuria (AMH) is a specific type of hematuria where small amounts of blood are detected only when viewed under a microscope. This condition is frequently discovered incidentally during routine health examinations or tests for other medical concerns.
Defining Asymptomatic Microscopic Hematuria
The term “asymptomatic” indicates that individuals do not experience noticeable symptoms like pain, visible blood, or difficulty urinating. This means the condition often goes unnoticed without specific medical testing.
The “microscopic” aspect means red blood cells in the urine are too few to be seen by the naked eye, identified instead through urinalysis. The American Urological Association (AUA) defines microscopic hematuria as three or more red blood cells per high-power microscopic field in urinary sediment from two out of three properly collected urine samples. This threshold helps differentiate a true finding from minor variations.
Potential Causes of Blood in Urine
Asymptomatic microscopic hematuria can stem from various sources, from benign conditions to more serious issues within the urinary tract. Common benign causes include vigorous physical activity, certain medications like blood thinners, or temporary dehydration. Menstrual blood or menopausal changes can also lead to false positive results on urine tests.
Urinary tract infections (UTIs) are a frequent cause, as bacteria irritate the urinary system. Kidney stones, hard mineral deposits, can also cause bleeding as they pass through or irritate the urinary tract. In men, an enlarged prostate (benign prostatic hyperplasia or BPH) can contribute to hematuria due to pressure on the urethra.
Various kidney diseases, such as glomerulonephritis (inflammation of the kidney’s filtering units), can also result in hematuria. Less commonly, asymptomatic microscopic hematuria can be an early indicator of conditions like bladder or kidney cancer. The risk of malignancy increases in individuals over 35, men, and those with a history of smoking.
Diagnostic Steps and Evaluation
Once asymptomatic microscopic hematuria is detected, a healthcare provider initiates a diagnostic process to identify the underlying cause. The initial step involves repeating the urinalysis to confirm hematuria’s persistence, as a single positive result may be transient. If confirmed, further evaluation is indicated.
Blood tests are performed to assess kidney function, measuring serum creatinine and estimated glomerular filtration rate (eGFR). A urine culture is also conducted to rule out a urinary tract infection, which, if present, requires antibiotic treatment. Imaging studies of the urinary tract are a subsequent step.
Common imaging techniques include kidney and bladder ultrasound, detecting kidney stones, structural abnormalities, or masses. A computed tomography (CT) urogram may also be used to identify stones, tumors, or lesions in the kidneys, ureters, and bladder. In some cases, a cystoscopy may be performed, especially for individuals over 35 or those with bladder cancer risk factors. This procedure involves inserting a thin, lighted tube with a camera into the urethra to directly examine the lining of the urethra and bladder.
What to Expect After Diagnosis
Following the diagnostic evaluation for asymptomatic microscopic hematuria, several outcomes are possible. Often, a specific cause is not identified, even after a thorough workup. These cases are referred to as “idiopathic” or “benign familial hematuria” and require periodic monitoring, such as repeat urinalysis at 6, 12, and 24 months.
If a cause is identified, such as a urinary tract infection, kidney stone, or a specific kidney disease, treatment is tailored to address that condition. For example, antibiotics are prescribed for a UTI, or interventions planned for kidney stones. While microscopic hematuria warrants investigation to exclude serious conditions, it is often benign or treatable. Consistent follow-up with a healthcare provider is important to manage the condition.