Urothelial cells, also known as transitional cells, are a specialized type of epithelial cell. They form a protective lining within the body, separating internal tissues from external environments or internal cavities.
The Urothelial Barrier
Urothelial cells are found lining the inside of the urinary tract, specifically covering the renal pelvis in the kidneys, the ureters, the bladder, and the urethra. This multi-layered lining is collectively known as the urothelium. The urothelium acts as a barrier, preventing urine and potential harmful substances or germs from passing from the urinary tract into the bloodstream and surrounding tissues.
A characteristic of urothelial cells, particularly those in the bladder, is their ability to stretch and recoil. This flexibility allows the bladder to expand significantly as it fills with urine and then return to its original shape upon emptying, all while maintaining an impermeable seal. The outermost layer consists of large, dome-shaped “umbrella cells” that are tightly packed, contributing to this protective and adaptable barrier function.
Analyzing Urothelial Cells in Urine
During a urinalysis, a common urine test, a small number of urothelial cells can normally be observed. These cells shed naturally as part of the body’s routine cell turnover, similar to skin cells. When a lab report indicates “few” urothelial cells, this is considered a normal finding.
If a report indicates “moderate” or “many” urothelial cells, it suggests increased shedding. This elevated count points to irritation or inflammation within the urinary tract. While an increased number of cells can be a sign of an issue, it does not, by itself, provide a specific diagnosis.
Lab reports might also use the term “atypical” to describe urothelial cells. Atypical cells appear unusual under a microscope, exhibiting differences in size, shape, or nuclear features like an enlarged nucleus or irregular membrane. The presence of atypical cells suggests further investigation is warranted, as these changes can be associated with more significant conditions.
Health Conditions Affecting the Urothelium
An increased presence of urothelial cells in urine can be linked to several conditions. Urinary tract infections (UTIs) are a frequent cause, as inflammation from bacterial invasion can lead to increased shedding. Conditions like cystitis (bladder inflammation) or urethritis (urethra inflammation) also result in higher cell counts.
The presence of kidney or bladder stones can also irritate the lining of the urinary tract, causing more urothelial cells to detach and appear in urine. This mechanical irritation triggers a reactive shedding response from the urothelium. While less common, certain medical treatments or chronic inflammation can similarly affect the urothelium, leading to changes in cell appearance or shedding patterns.
Urothelial carcinoma, a type of cancer that begins in these cells, is a more serious, but less common, condition. This cancer can originate in the bladder, ureters, or renal pelvis, involving the uncontrolled growth of urothelial cells. Risk factors include smoking, exposure to certain industrial chemicals like aromatic amines, and chronic bladder inflammation.
Diagnostic Procedures for Urothelial Issues
When abnormal urothelial cell findings appear in a urine test, healthcare providers recommend further diagnostic steps to determine the underlying cause. Urine cytology is a common follow-up test, where a pathologist microscopically examines urine samples for cancerous or precancerous cells. While highly specific in identifying malignant cells, cytology can have lower sensitivity, particularly for low-grade tumors.
Another procedure is cystoscopy, which involves inserting a thin, flexible tube with a camera (cystoscope) through the urethra to visually inspect the inside of the bladder and urethra. This allows the doctor to directly observe any abnormal areas, growths, or sources of irritation. During a cystoscopy, a biopsy may be performed, involving the removal of a small tissue sample for detailed microscopic analysis.
Imaging tests, such as a CT urogram or MRI, may also be used to visualize the entire urinary tract, including the kidneys and ureters, to identify any abnormalities that might not be visible during a cystoscopy. These comprehensive evaluations help pinpoint the source of urothelial changes and guide appropriate management or treatment.