Transitional epithelial cells (also called urothelial cells) line the bladder, ureters, and part of the urethra. A small number shedding into the urine is normal as these cells naturally turn over. Increased numbers can appear with urinary tract infections, kidney stones, or recent instrumentation like catheterization. Rarely, abnormal-looking transitional cells can be a clue to a urinary tract tumor, which is why their appearance, not just their number, is noted. They are interpreted in the context of symptoms and the rest of the urinalysis.

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