Epithelial cells are specialized cells that form the protective lining for the internal and external surfaces and cavities of the body. These cells act as a barrier against pathogens and contribute to filtration processes throughout the body. Their presence in a urine sample is a common finding during a standard urinalysis test. Epithelial cells naturally shed from the lining of the urinary tract as part of routine cell turnover. Finding a small number of these cells does not typically indicate an issue, but their analysis provides important information about the health of the urinary system.
The Origin of Epithelial Cells in Urine
The epithelial cells found in a urine sample originate from various points along the pathway that urine travels through to exit the body. The entire urinary system, from the kidneys down to the external opening of the urethra, is lined with epithelial tissue. As cells age, they naturally detach from this lining and are carried away in the urine.
Identifying the cell type helps pinpoint the potential source. The upper urinary tract (kidneys and ureters) is structurally distinct from the lower tract (bladder and urethra). This continuous process of normal cell sloughing makes the presence of some epithelial cells an expected finding in any urine specimen.
Identifying the Types of Epithelial Cells
Microscopic examination of urine can distinguish three main classifications of epithelial cells, each originating from a different part of the genitourinary system.
Squamous Epithelial Cells
These are the largest and flat cells with an irregular shape. They typically originate from the lower urethra or the external genitalia. Their presence is often associated with contamination during the sample collection process.
Transitional Epithelial Cells
Also known as urothelial cells, these line the renal pelvis, ureters, and bladder. They are smaller than squamous cells and may appear round, pear-shaped, or polygonal. An increased number of transitional cells can result from inflammation or irritation within the urinary tract, such as from catheterization.
Renal Tubular Epithelial Cells (RTE)
RTEs originate specifically from the tubules within the kidneys. These cells are small, round, or columnar. They are the most significant type for interpretation because their source is the kidney itself. The presence of RTEs in the urine often suggests injury or damage occurring directly within the kidney structures.
What Counts as a Normal Result
A normal finding in a urinalysis report indicates a low number of epithelial cells, consistent with the natural shedding of cells from the urinary tract lining. Results are commonly reported using qualitative terms such as “few,” “moderate,” or “many” per high-power field (HPF) under the microscope. Finding a report that states “few” epithelial cells is usually considered within the expected range.
Numerically, a count of zero to five epithelial cells per HPF is often cited as a normal baseline. This low count, particularly when the cells are predominantly squamous, is generally considered clinically insignificant and does not automatically imply a disease or disorder.
When Elevated Cells Signal a Problem
An elevated count of epithelial cells, reported as “moderate” or “many,” can signal an underlying health issue. The specific type of cell that is elevated provides the most diagnostic information.
Squamous Cell Elevation
A high concentration of squamous epithelial cells most often indicates a poorly collected specimen that was contaminated by external skin cells.
Transitional Cell Elevation
Increased numbers of transitional epithelial cells may point to inflammation or irritation within the lower urinary tract, such as the bladder. This is a common feature of a urinary tract infection (UTI). If a high transitional cell count is present alongside white blood cells and bacteria, a diagnosis of cystitis or another inflammatory condition is likely.
Renal Tubular Epithelial Cell (RTE) Elevation
The appearance of a significant number of RTEs, exceeding 15 cells per HPF, is the most concerning finding and suggests injury to the kidney’s filtering units. This increase can be a marker for serious conditions, including acute tubular necrosis or interstitial nephritis. The presence of RTEs, especially when seen with other elements like granular casts, indicates kidney disease or damage.