Epithelial cells are the individual cells that make up the tissue known as epithelium. Epithelium is the tissue that covers the body inside and out, including the urinary tract. It is normal for some of these cells to be sloughed off into the urine and be noted during the microscopic examination of a routine urinalysis.
The last step in a complete urinalysis is the microscopic examination of urine sediment. This reveals not only the presence or absence of any epithelial cells, but also how many and what types of cells are present.
Three main types of epithelial cells line the urinary tract: squamous, transitional and renal tubular cells. They are named according to their location and their function, and are usually quantified by "occasional, few, moderate or many."
Squamous epithelial cells are found in the vagina, outer urethra and on the skin surface. Transitional epithelial cells are found in the bladder, renal pelvis and ureter. Renal tubular cells are found in the nephrons of the kidney.
It is normal not to have any epithelial cells present in a urine sample or to have occasional numbers of any of the three cell types. Large numbers of squamous cells may indicate contamination of the urine specimen, but large numbers of either the transitional or renal tubular cells may indicate a serious disease process.
Following instructions given to you for proper collection of a urine sample for a urinalysis will produce a sample free of contamination by squamous epithelial cells. If any of the other two cell types are present in numbers other than "occasional or few" your doctor may request additional testing.