A urinalysis includes a battery of chemical tests and often a microscopic examination of the urine. This allows for the detection of various microscopic solids in the urine, including crystals, bacteria, red blood cells, white blood cells and epithelial cells. Different types of epithelial cells form the superficial skin layers and line the various structures of the urinary system and genitals. In most cases, the presence of epithelial cells in the urine is a normal finding. The presence of certain types of epithelial cells in significant numbers, however, can indicate a urinary tract problem.
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You're probably aware that the cells of your skin surface regularly shed and are replaced. The same process, called sloughing, occurs with the epithelial cells of various urinary tract structures. Thus, the presence of epithelial cells in the urine often indicates normal sloughing. A cell type called squamous epithelial cells are usually most abundant in the urine and come primarily from the urinary bladder, female labia, male foreskin, vaginal secretions and urethra (the tube through which urine flows out of the bladder). A few epithelial cells from higher in the urinary tract and kidneys -- called transitional and renal tubular epithelial cells -- also sometimes appear in the urine due to normal sloughing.
While squamous epithelial cells in the urine are usually a normal finding, clue cells are an exception. These are squamous cells from the vagina covered with bacteria called Gardnerella vaginalis, which typically signals a condition called bacterial vaginosis (BV). With BV, these bacteria firmly adhere to the epithelial cells lining the vagina -- even after they have been sloughed. As vaginal discharge is increased with BV, it's common for some vaginal secretions to contaminate the urine during specimen collection.
Increased numbers of squamous and/or transitional epithelial cells can occur with a urinary tract infection (UTI), including a bladder or a kidney infection. People with a UTI also typically have high numbers of white blood cells and bacteria present on microscopic examination of the urine, which helps confirm the diagnosis.
Kidney Damage or Disease
The presence of more than a few renal tubular epithelial cells usually signals injury to the renal tubules due to kidney damage or disease. These tiny structures perform much of the critical work of the kidneys, retaining important substances such as blood sugar, proteins and electrolytes while eliminating metabolic waste products. The renal tubules also help maintain water, pH and electrolyte balance in the body. Conditions that can lead to the presence of significant numbers of renal tubular epithelial cell in the urine include:
- Extreme blood loss and/or low blood pressure
- Use of kidney-toxic medications
- Aspirin overdose
- Accidental exposure to kidney-toxic poisons or heavy metals
- Blood transfusion reaction
- Massive muscle damage
- Certain viral infections
- Kidney transplant rejection
- Kidney cancer
In most cases, the presence of epithelial cells in the urine is normal and does not indicate an underlying problem. However, if the number or type could potentially signal a problem, your healthcare provider will consider the other results of the urinalysis. If the diagnosis is uncertain, she might order a repeat urinalysis and possibly additional tests to determine the cause and appropriate treatment, if needed.
Reviewed and revised by: Tina M. St. John, M.D.