A urinalysis is a noninvasive urine screening test in which a patient urinates into a small receptacle. A lab technician then examines the urine on several levels. Visual analysis of urine can yield observations about color and clarity, while chemical analysis checks for acidity and density. Many urinalysis tests also include a microscopic exam of the urine, through which the technician can check for blood cells, large particles, and epithelial cells, which compose the surface membranes of the urinary tract and kidneys.
Most epithelial cells in urine are the result of normal sloughing of epithelial tissue, according to Cornell University, and don't indicate anything abnormal. The ureters, which carry urine from the kidneys to the bladder, the bladder itself, and the urethra, which carries urine outside the body, are all lined with epithelial tissue. Like skin, this tissue constantly sloughs and is replaced to keep it fresh and viable. Sloughing cells end up in the urine, though usually in small concentrations, and are excreted. According to the university, it's even routine to find epithelial cells characteristic of the female reproductive tract in female urine, since urine must contact the external genital mucous membranes, including the labia minora, on its way out of the body.
The University of Utah School of Medicine suggests that while a relatively small number of epithelial cells in a urine sample isn't remarkable, cells present in large numbers may indicate kidney problems. Particularly if the cells in question have morphological characteristics that identify them as renal tubule cells, including a round shape and large nuclei, cells may be a sign of nephrotic syndrome. This syndrome is the result of largely nonspecific kidney damage, and includes degeneration of the small tubes, called renal tubules, that carry filtered blood through the microanatomy of the kidney. Since renal tubule function is essential to urine production--it's in the tubules that vital molecules are resorbed from the liquid and toxins are concentrated--renal tubule degeneration can be quite serious.
Urinary Tract Infection
Lab Tests Online, an Internet site with information about lab tests and how they're performed, notes that urinary tract infections represent yet another potential source of large numbers of epithelial cells in urine. Most urinary tract infections begin in the bladder, after bacteria--mainly E. coli--climb the urethra into the bladder. Once bacteria colonize the bladder epithelium, they irritate it and cause increased epithelial sloughing relative to normal. Serious infections can ascend the ureters and reach the kidneys, causing sloughing of the upper urinary tract. The website notes that identifying which kind of epithelial cells are in the urine is medically useful, since it helps physicians determine the level and extent of an infection.