Urothelial Cells in Urine: What Do Your Results Mean?

Finding urothelial cells in your urine is, in most cases, completely normal. These cells form the inner lining of your bladder, ureters, and urethra, and they naturally shed into urine as part of routine tissue turnover. What matters on a lab report is not whether urothelial cells are present, but how many there are and whether they look unusual under a microscope. A small number of ordinary-looking urothelial cells is expected; a large number, or cells with abnormal features, can signal anything from a urinary tract infection to something that needs closer investigation.

What Urothelial Cells Are and Why They Shed

The urothelium is a specialized tissue that lines nearly the entire urinary tract, from the inside of the kidneys’ collecting system down through the ureters, across the bladder, and into the urethra. Its primary job is acting as a barrier: it keeps the concentrated, sometimes toxic contents of urine from seeping into surrounding tissue. The surface layer of this lining is made up of large, umbrella-shaped cells that stretch and compress as the bladder fills and empties. Over time, these surface cells wear out and are replaced by cells from deeper layers pushing upward. That natural turnover is why a routine urinalysis almost always picks up at least a few urothelial cells.

The shedding process is not just passive wear and tear. During a bladder infection, the body actively sheds infected surface cells as a defense strategy. Research has shown that during cystitis, mast cells migrate directly underneath the superficial bladder lining, dock against it, and release granules that trigger the infected cells to detach and wash away with urine.

1PubMed Central. Loss of Bladder Epithelium Induced by Cytolytic Mast Cell Granules

This is a clever trick: the body sacrifices a layer of barrier cells to flush out bacteria. But it also means that an active infection will dramatically increase the number of urothelial cells in your urine sample, sometimes accompanied by white blood cells and bacteria.

Common Reasons for Elevated Urothelial Cells

If your lab report notes a higher-than-expected count of urothelial cells, the most likely explanations are benign. Urinary tract infections are the leading cause. In people with chronic or recurrent UTIs, ongoing inflammation can damage the bladder lining enough to cause persistent shedding. Studies of bladder tissue from patients with recurrent lower urinary tract infections have found significant loss of the urothelial lining compared to healthy controls, with chronic inflammation linked to increased cell death and disruption of the barrier’s integrity.

2International Continence Society. Loss of urothelium in recurrent lower urinary tract infections

Beyond infections, several other everyday situations can elevate your urothelial cell count:

  • Catheterization: Inserting a urinary catheter physically scrapes cells off the urethra and bladder wall. Samples collected this way often show more urothelial cells than a midstream clean-catch specimen.
  • Kidney stones: A stone passing through the ureter or sitting in the bladder irritates the lining and causes localized shedding.
  • Interstitial cystitis: This chronic bladder pain condition involves inflammation of the bladder wall. Patients with interstitial cystitis show altered protein expression in their urothelial cells, reflecting ongoing damage to the lining.
    • 3PubMed Central. Changes in uroplakin expression in the urothelium of patients with ulcerative interstitial cystitis/bladder pain syndrome
  • Recent procedures: Cystoscopy, bladder biopsies, or any instrumentation of the urinary tract will temporarily increase cell shedding.

In all of these scenarios, the cells themselves typically look normal under a microscope. The elevated count reflects irritation or trauma to the lining, not a problem with the cells themselves.

What “Atypical Urothelial Cells” Means on Your Report

The word that tends to alarm people is “atypical.” When a cytopathologist examines your urine sample under a microscope, they assess each urothelial cell’s shape, size, and nuclear features. Normal urothelial cells have small, uniform nuclei relative to their overall cell size. Atypical cells show changes that fall into a gray zone: they do not look entirely normal, but they also do not clearly look cancerous.

The classification system most labs use today is called the Paris System for Reporting Urinary Cytology. Under this framework, the key feature that pushes a cell into “atypical” territory is an increased ratio of nucleus to cytoplasm, specifically when the nucleus takes up at least half but less than about 70 percent of the cell’s area. Additional warning signs include darker-than-normal nuclei, irregular nuclear borders, and coarse or clumpy chromatin patterns.

4Journal of Clinical and Translational Pathology. The Paris System for Reporting Urinary Cytology: An Updated Review

Getting an “atypical urothelial cells” result does not mean you have cancer. It means the cells look unusual enough that your doctor will want to investigate further, usually with cystoscopy, where a thin camera is threaded into the bladder to look directly at the lining. Many atypical results turn out to be caused by inflammation, recent infections, or instrumentation. But because a small percentage of atypical results do eventually lead to a cancer diagnosis, follow-up is standard practice.

5PubMed. Clinical follow up and the impact of the Paris system in the assessment of patients with atypical urine cytology

The Cancer Screening Role of Urine Cytology

Urine cytology has been used for decades to screen for and monitor bladder cancer, which arises from the urothelial lining. Its greatest strength is catching high-grade urothelial carcinoma: the more abnormal the cancer cells, the easier they are to spot under a microscope. When cells have very large, dark, irregular nuclei relative to the cytoplasm, a trained pathologist can identify them with reasonable confidence.

The challenge lies in lower-grade tumors, where the cancer cells look much closer to normal urothelial cells. One study analyzing how well pathologists agree when grading urothelial carcinoma on urine cytology found that overall accuracy was about 77 percent, but agreement between individual pathologists was often low, with most comparisons falling below the threshold considered “fair” agreement.

6PubMed Central. Accuracy of grading of urothelial carcinoma on urine cytology: an analysis of interobserver and intraobserver agreement

This is a known limitation. Urine cytology is good at confirming high-grade disease but less reliable at distinguishing low-grade cancer from benign reactive changes. That inconsistency is one reason your doctor might order additional tests even when cytology looks reassuring.

Differentiating cancer cells from other look-alikes can require specialized staining techniques. Reactive kidney tubular cells, which can slough into urine during kidney injuries or infections, sometimes resemble low-grade cancer cells. Immunostaining studies have shown that these kidney-origin cells stain strongly for a protein called vimentin (positive in nearly all cases) while being negative for a marker called 34βE12. Low-grade urothelial carcinoma cells show the opposite pattern: negative for vimentin, with a smaller proportion staining positive for 34βE12.

7PubMed Central. Expression of vimentin and high-molecular-weight cytokeratin (clone 34ßE12) in differentiating reactive renal tubular cells from low-grade urothelial carcinoma cells in voided urine

In practice, this means that when a pathologist sees suspicious cells in your urine, they have tools beyond just looking at shape to figure out what those cells actually are.

When Viruses Change How Urothelial Cells Look

Not every alarming-looking cell in urine is related to cancer or infection by bacteria. Certain viruses, most notably BK virus, can cause urothelial cells to develop features that mimic malignancy. These virus-altered cells are known as “decoy cells” precisely because they can fool pathologists into thinking something more sinister is going on.

BK virus is extremely common: most people are infected during childhood and carry the virus in a dormant state in their urinary tract for life. It only becomes a problem when the immune system is suppressed, which is why decoy cells are most frequently seen in kidney transplant recipients taking anti-rejection medications. In these patients, BK virus can reactivate, infect urothelial cells, and cause them to develop enlarged nuclei with a distinctive “ground-glass” appearance and a high nucleus-to-cytoplasm ratio.

8Journal of Pathology and Translational Medicine. Urinary Decoy Cell Grading and Its Clinical Implications

Decoy cells are considered one of the earliest markers of BK virus reactivation and can be spotted in urine sediment, sometimes even without special staining.

9PubMed Central. Bright Field Microscopy to Detect Decoy Cells Due to BK Virus Infection in the Fresh and Unstained Urine Sediment in Kidney Allograft Recipients

The clinical importance is significant: unchecked BK virus reactivation can damage a transplanted kidney. Identifying decoy cells in urine triggers further testing, typically a blood test measuring viral DNA levels, and may prompt doctors to reduce immunosuppressive medication. Decoy cells have also been reported after stem cell transplantation, confirming that any severe immunosuppression can set the stage for BK virus to emerge.

10PubMed Central. Decoy cells detected in the urine of a patient with complex karyotype Myelodysplastic neoplasms who underwent umbilical cord blood transplantation: a case report

If you are not immunosuppressed and your lab report mentions unusual-looking urothelial cells, BK virus is far less likely to be the explanation. But for transplant patients, decoy cell screening in urine is a routine and important part of post-transplant monitoring.

How Cancer Treatments Can Muddy the Picture

People who have been treated for bladder cancer, or who have received radiation to the pelvic area for other cancers, face a specific interpretive challenge: their treatments can make normal urothelial cells look abnormal. Chemotherapy drugs (both those instilled directly into the bladder and those given through an IV), radiation therapy, immunotherapy with BCG, and even photodynamic therapy all produce recognizable changes in the urothelial lining. These treatment-related changes can mimic the appearance of cancer cells.

11PubMed Central. Changes produced in the urothelium by traditional and newer therapeutic procedures for bladder cancer

Radiation is a particularly well-known offender. In one study that prospectively evaluated urine samples from patients receiving pelvic radiation, roughly two-thirds of post-treatment samples showed cellular changes consistent with radiation exposure, even though none contained actual malignant cells.

12PubMed. Prospective evaluation of the effect of ionizing radiation on the bladder tumor-associated (BTA) urine test

Radiation-induced changes can persist for months or even years after treatment ends. For patients being monitored for cancer recurrence, this creates a real headache: the very surveillance tool meant to catch returning cancer is partly blinded by the effects of the treatment that dealt with it in the first place. Pathologists who know a patient’s treatment history can often distinguish therapy-related changes from true recurrence, which is one reason your clinical context matters enormously when interpreting urine cytology results.

Occupational Exposures and Urothelial Screening

Certain workplace exposures are known to increase bladder cancer risk, and urine cytology has been explored as a screening tool in these populations. Workers in the textile dyeing industry, for example, face long-term exposure to aromatic amines, chemicals that are metabolized and concentrated in urine, where they can damage the urothelial lining over years. A study of exposed textile workers found that those with more than ten years of cumulative exposure were the ones who showed concerning cytology results, including atypical urothelial cells and cells suspicious for high-grade cancer. Among these workers, subsequent imaging and cystoscopy revealed actual bladder tumors in a small number of cases.

13IntechOpen. Textile Dye Exposure as an Occupational Hazard Risk for Bladder Cancer

This is worth knowing because bladder cancer has a well-established link to occupational chemical exposure, not just to smoking (which remains the single largest risk factor). If you work in an industry that involves dyes, rubber manufacturing, certain paints, or other chemical processes, and your urine results show atypical cells, your doctor should be told about your occupational history. It changes how aggressively they pursue follow-up.

When the Problem Is Higher Up

Most discussion of urothelial cells in urine focuses on the bladder, but the same type of lining extends up through the ureters and into the renal pelvis of each kidney. Cancers arising in these upper tract locations are less common but can also shed abnormal cells into urine. The difficulty is that standard voided urine cytology is less sensitive for upper tract disease because the cells have a longer journey and may degrade before reaching the collection cup.

Research has shown that the sensitivity of urine cytology alone for detecting high-grade upper tract urothelial carcinoma is about 65 percent, and ureteroscopic biopsy alone catches roughly 59 percent. Neither test is great by itself. But combining the two pushes sensitivity up to about 86 percent, a significant improvement.

14PubMed Central. Diagnostic role of urine cytology and ureteroscopic biopsies in detection of high grade upper tract urothelial carcinoma

For upper tract evaluation, some centers also collect “washing” specimens, where saline is flushed through a catheter threaded up into the ureter or renal pelvis, then collected for analysis. These specimens tend to contain more cells and better-preserved cells than voided urine.

15CytoJournal. Upper tract urinary cytology to detect upper tract urothelial carcinoma: Using the Johns Hopkins Hospital template and evaluation of its feasibility

If your doctor suspects an upper tract issue, they will not rely on a standard urine sample alone. Imaging studies and direct visualization with a scope are typically part of the workup.

Newer Tests Moving Beyond the Microscope

Traditional urine cytology depends on a human being looking at cells under a microscope and making a judgment call. That approach has been the standard for decades, but it has clear limitations: it is subjective, less sensitive for low-grade tumors, and affected by specimen quality. A wave of newer molecular and automated tests is starting to change the landscape.

Several molecular tests designed to detect bladder cancer markers in urine are now clinically available. Tests like Cxbladder, Bladder EpiCheck, and UroSEEK analyze DNA, RNA, or protein markers shed by tumor cells, offering higher sensitivity than cytology for certain types of bladder cancer.

16PubMed Central. Novel Urinary Biomarkers for the Detection of Bladder Cancer

These are not replacements for cystoscopy yet, but they are increasingly used alongside traditional methods, particularly for patients being monitored after a previous bladder cancer diagnosis. The appeal is obvious: a urine test that can reliably detect early recurrence could reduce the frequency of uncomfortable cystoscopy procedures.

Automated urine analyzers are also becoming more sophisticated. Flow cytometry-based instruments can flag suspicious cells in real time by measuring their size, shape, and fluorescence properties. One study evaluating the UF-5000 flow cytometer found that its agreement with traditional cytopathology was about 73 percent, with a sensitivity of 59 percent and specificity of 82 percent for detecting urothelial carcinoma.

17PubMed Central. Investigation of Atyp.C using UF-5000 flow cytometer in patients with a suspected diagnosis of urothelial carcinoma: a single-center study

Those numbers are not high enough to replace expert pathology review, but they are useful as a first-pass screening tool that can prioritize which samples need the most careful human attention. The technology is improving, and it is reasonable to expect that within the coming years, the combination of molecular markers and automated analysis will make urine-based diagnosis faster, more consistent, and less dependent on individual pathologist interpretation.

Tissue Engineering and the Future of the Urothelium

Research into urothelial cells extends well beyond diagnosis. Scientists have been working on growing urothelial tissue in the lab, with the eventual goal of reconstructing damaged or diseased bladders. Combining stem cells with specialized scaffolding materials has shown promise in animal models, and the concept of building a functional bladder from a patient’s own cells is no longer pure science fiction. That said, the gap between laboratory success and routine clinical use remains wide. The bladder is a mechanically complex organ that must stretch, contract, and maintain a watertight seal, and replicating all of those properties in engineered tissue is an enormous challenge that has not yet been solved for widespread use.

18PubMed Central. Tissue engineering of urinary bladder – current state of art and future perspectives

For now, the practical relevance for most people is simpler: the urothelial cells that show up in your urine sample are a window into the health of a tissue you rarely think about until something goes wrong. A handful of normal-looking cells is just your bladder doing routine housekeeping. Changes in number, shape, or nuclear features tell your doctor whether the lining is irritated, infected, reacting to medication, or in rare cases, developing something that needs treatment. The clinical context around the sample, your symptoms, medical history, medications, and risk factors, matters just as much as what the cells look like under a microscope.