A urinalysis is a standard medical test that provides a microscopic view of the components present in a urine sample, including epithelial cells. These cells line the surfaces and hollow structures throughout the body, such as the entire urinary tract. While their appearance on a lab report can cause concern, finding a small number of epithelial cells is common and expected. The significance of this finding depends on the specific type and quantity of cells identified by the laboratory.
What Are Epithelial Cells and Why Are They in Urine?
Epithelial cells form a protective barrier lining the skin and internal passages, including the kidneys, ureters, bladder, and urethra. This tissue layer (epithelium) guards underlying tissues against pathogens, damage, and the harsh chemical environment of urine, constantly undergoing natural renewal.
During this process, older or damaged cells detach from the lining and are flushed out with the urine. This normal shedding is why a few epithelial cells are routinely found in nearly every urine sample. Therefore, their simple presence is not an indication of a medical problem. Analysis focuses on whether the rate of shedding is abnormally increased due to irritation, inflammation, or damage.
The Three Types of Epithelial Cells Found in Urine
The urinary tract is lined by three distinct types of epithelial cells. Identifying the type present helps determine the cell’s origin and potential clinical meaning.
Squamous Epithelial Cells
Squamous cells are the largest type and possess a characteristic flat, thin, and irregular shape. They originate from the lower part of the urinary tract, such as the distal urethra, and from the external genitalia. Finding a small amount of these cells is generally considered normal, but a high number often indicates that the urine sample was contaminated with cells from the skin during collection.
Transitional (Urothelial) Cells
Transitional epithelial cells, also known as urothelial cells, line the renal pelvis, ureters, bladder, and part of the urethra. These cells are distinct because they can change shape, stretching to accommodate the filling and emptying of the bladder. An increased presence of these cells frequently suggests inflammation or irritation in the lower urinary tract, such as the bladder.
Renal Tubular Cells
Renal tubular epithelial cells are the smallest and most clinically significant type found in urine. They originate directly from the tiny filtering tubules within the kidneys. The presence of these cells, even in small clusters or numbers, is a strong indicator of injury or disease affecting the kidney itself.
Interpreting Epithelial Cell Counts
A urinalysis report quantifies epithelial cells using subjective terms or counts per microscopic field. A report stating “few” or “rare” cells typically represents a normal finding, often equating to less than five cells per high-power field (HPF). This range reflects the routine turnover of the urinary tract lining.
A finding of “moderate” or “many” cells, often exceeding 15 to 20 cells per HPF, is considered elevated and suggests further investigation. If the elevated count consists primarily of squamous cells, the most probable explanation is contamination due to improper collection technique. Proper “clean catch” collection, which involves cleaning the genital area and collecting a midstream sample, helps minimize this contamination.
When transitional or renal tubular cells are elevated, the finding signals a potential issue within the urinary system itself. Interpretation depends not only on the raw number but also on the cell type and the presence of other elements like bacteria or white blood cells.
Medical Conditions Associated with Elevated Counts
The clinical significance of an elevated epithelial cell count is determined by the specific cell type involved. A high count of transitional epithelial cells is linked to irritation or inflammation of the bladder lining, often caused by a urinary tract infection (UTI). In a UTI, the infection triggers the bladder lining to shed cells at an accelerated rate.
Physical irritation from stones, such as kidney or bladder stones, can also cause increased shedding of transitional cells as they scrape against the urinary tract walls. Severe dehydration can also lead to highly concentrated urine, which may temporarily increase the rate of epithelial cell shedding.
The presence of numerous renal tubular epithelial cells points to direct injury to the kidney. Conditions such as acute tubular necrosis, a form of kidney failure, or inflammatory kidney diseases like nephritis, cause these kidney-specific cells to slough off in large numbers. A high count of renal tubular cells signals potential kidney disorder and requires medical follow-up.