A urinalysis is a common diagnostic test used to assess the health of the urinary tract and kidneys. It involves a microscopic examination of a urine sample, including different types of cells. Epithelial cells form the protective lining of the entire urinary system. While finding these cells often causes concern, a small number is normal and expected. Correctly interpreting the results requires understanding the specific type and quantity of cells present.
What Epithelial Cells Are and Why They Appear in Urine
Epithelial cells are specialized cells that create a continuous barrier lining the urinary system, extending from the kidneys to the urethra. Their primary function is to provide a protective layer against pathogens and harmful substances. As part of the body’s natural regeneration cycle, these cells are continuously shed and replaced. This normal cellular turnover explains why a few epithelial cells are almost always present in any urine sample.
A standard microscopic urinalysis identifies these cells by examining the urine sediment under a high-power field (HPF) microscope. The presence of a few cells, typically reported as “rare” or “few” (less than five cells per HPF), is considered a normal finding. However, irritation, inflammation, or damage to the urinary tract increases the rate of cell shedding dramatically. This accelerated shedding leads to a report of “moderate” or “many” epithelial cells, signaling a potential underlying issue.
The Three Types of Epithelial Cells and Their Origin
The significance of epithelial cells depends entirely on their specific type, which indicates their point of origin within the urinary tract. The three primary classifications are squamous, transitional, and renal tubular epithelial cells.
Squamous Epithelial Cells
Squamous cells are the largest type, often flat and irregularly shaped, originating from the outer urethra and external genitalia. Due to their location, they are the most commonly seen type, especially in female samples. High numbers usually indicate contamination of the sample from the skin during collection and hold the least clinical significance.
Transitional Epithelial Cells
Transitional cells, also known as urothelial cells, line the urinary tract from the renal pelvis, down the ureters, and into the bladder. These cells are smaller than squamous cells and are characterized by a round or pear-like shape. While a few shed normally, elevated numbers often suggest irritation or inflammation within the bladder or upper urinary tract.
Renal Tubular Epithelial (RTE) Cells
RTE cells are the smallest and most clinically important type, originating from the tubules within the kidneys. These tubules are responsible for filtering blood and reabsorbing essential nutrients. Even a small number of RTE cells is highly significant because their presence is a strong marker for damage to the kidney tissue itself.
Clinical Implications of High Epithelial Cell Counts
A high number of epithelial cells is meaningful only when correlated with the specific cell type and other findings in the urinalysis. High counts of squamous cells are usually attributed to improper collection technique and are typically a technical issue rather than a sign of disease.
When transitional (urothelial) cells are significantly elevated, it often points toward inflammation or infection in the lower urinary tract, such as cystitis. Bacterial urinary tract infections irritate the bladder lining, causing increased sloughing of these cells. High numbers of transitional cells can also be seen following trauma, such as the passing of a kidney stone or irritation from a urinary catheter.
A high count of RTE cells, generally defined as more than 15 cells per HPF, is a direct indicator of injury to the kidney’s filtering units. This finding is a hallmark sign of acute tubular necrosis, a serious condition where kidney tubules are damaged by lack of oxygen, toxins, or certain medications. Severe kidney disorders, such as glomerulonephritis, can also lead to increased shedding of RTE cells.
In rare instances, a markedly increased presence of transitional cells that appear abnormal or “atypical” may warrant investigation for malignancy, such as bladder cancer. Determining the exact cause of elevated cell counts always requires considering the overall clinical picture, including patient symptoms and other laboratory values.
When to Seek Medical Consultation
Interpreting a urinalysis report requires integrating the epithelial cell count with the patient’s symptoms and other findings, such as the presence of white blood cells, bacteria, or protein. If your report indicates “many” or “numerous” epithelial cells, especially transitional or renal tubular types, consult with your healthcare provider. This consultation is crucial if the finding is accompanied by symptoms like painful urination, fever, flank pain, or cloudy urine.
The presence of any renal tubular epithelial cells warrants prompt medical follow-up due to its association with potential kidney injury. Even if the count is reported as “few,” the overall context matters, particularly if the sample was collected correctly using the clean-catch method. The doctor will use the epithelial cell result alongside other findings to determine if further diagnostic steps are necessary, such as a urine culture or blood tests to assess kidney function.