Urine Squamous Epithelial Test

When you get a urinalysis, one of the first things the lab checks is whether your sample is actually clean enough to trust. Squamous epithelial cells (SECs) are the main clue. These are large, flat cells that line the outer portion of your urethra and, in women, the vulva. Finding a few in your urine is normal. Finding a lot usually means skin cells washed into the cup during collection, making the rest of the results less reliable.

That matters because a contaminated sample can trigger a false alarm for infection or mask a real one. But squamous cells are not always just noise. In rare cases, abnormal-looking squamous cells point to something more serious happening inside the bladder or reproductive tract. Understanding this biomarker helps you know when to simply recollect your sample and when to pay closer attention.

What Counts as Normal

Labs typically report squamous epithelial cells either as a count per high-power microscope field (HPF) or as a concentration per microliter. On automated analyzers, the normal reference range is generally 7 to 8 cells per microliter or fewer, with no significant difference between men and women. You may also see results reported descriptively as "few," "moderate," or "many," where "few" is considered normal.

More than 5 squamous cells per HPF suggests your sample picked up cells from the genital area or the end of the urethra rather than from deeper in the urinary tract. For the most accurate results, especially when evaluating blood in the urine, a stricter threshold of 2 or fewer squamous cells per HPF has been proposed. Meeting that cutoff improves the reliability of detecting true microscopic hematuria in women.

Because men and women have different anatomy, gender-specific contamination cutoffs have also been suggested: more than 21 cells per microliter for women and more than 5 cells per microliter for men. If your result exceeds these thresholds, the sample may not reflect what is actually happening inside your urinary tract.

Contamination, Infection, or Something Else

Most of the time, elevated squamous cells simply mean the sample was not collected cleanly enough. But the relationship between squamous cells and urine culture results is not as straightforward as you might expect. Squamous cell counts turn out to be a relatively weak predictor of whether a urine culture will come back contaminated (the statistical accuracy is modest, with an area under the ROC curve of just 0.68). In other words, a high squamous cell count does not automatically mean your culture result is unreliable.

What elevated squamous cells do affect is how well the rest of the urinalysis performs. Samples with more than 8 squamous cells per HPF show noticeably lower accuracy for predicting bacterial infection, with specificity dropping from 84% down to 70%. That means a contaminated sample is more likely to falsely suggest an infection that is not there, potentially leading to unnecessary antibiotics or repeated testing.

Here is the important nuance: even when squamous cells suggest contamination, the presence of blood or white blood cells in your urine still warrants further evaluation. Those findings should not be dismissed just because the sample appears contaminated.

When Squamous Cells Signal Something Deeper

In a small number of cases, the squamous cells in your urine are not contaminants at all. They come from changes inside the urinary tract itself. Understanding where these cells can originate helps you recognize when a result might deserve a closer look rather than a simple recollection.

Normal shedding: In women, benign squamous cells commonly appear from three anatomic sites: the bladder trigone (the triangular area at the base of the bladder), the urethra, or the cervicovaginal region. These represent routine cellular turnover.

Squamous metaplasia: When the bladder lining is chronically irritated, whether from repeated infections, long-term catheter use, bladder stones, or parasitic infection (schistosomiasis), the normal bladder cells can gradually transform into squamous cells. This process is called squamous metaplasia. In regions where schistosomiasis is common, squamous metaplastic cells were found in roughly half of individuals with past or current infection, but in none without exposure.

Atypical squamous cells: This is the finding that matters most. Atypical squamous cells (ASCs) are rare, appearing in only about 0.3% of urine specimens, but they carry real clinical weight. These cells look different under the microscope: enlarged, darkly staining nuclei with irregular borders and a high ratio of nucleus to surrounding cell body. About 31% of people found to have ASCs are later diagnosed with squamous cell carcinoma of the bladder, urothelial carcinoma with squamous features, or cervical cancer.

A larger study looking at outcomes over ten years found that low-grade squamous atypia carried a 70% risk of being associated with high-grade malignancy, while high-grade atypia carried a 92% risk. When atypical squamous cells appeared alongside abnormalities in the bladder's own lining cells, the malignancy risk exceeded 90%. For women with atypical squamous cells in urine, a pelvic examination should be considered to rule out cervical pathology.

Complications of Persistent Squamous Changes

When squamous cells keep showing up because of true changes inside the bladder rather than contamination, the stakes rise considerably. The form that carries the most concern is keratinizing squamous metaplasia, where the transformed bladder cells begin producing keratin, the tough protein found in skin and nails. This is not just a cosmetic change to the tissue.

In a review spanning 54 years, keratinizing squamous metaplasia was identified as a significant risk factor for bladder cancer. The extent of involvement mattered greatly: when more than half of the bladder's inner surface was affected, 55% of those individuals went on to develop cancer. When the involvement was limited, the cancer rate was 12.5%. Other complications included bladder contracture and blockage of the ureters (the tubes connecting kidneys to bladder), which can impair kidney drainage.

Sources: Khan et al. (54-year review); Ho and Elsheikh (10-year urine cytology study); Pottegård et al. (Danish case-control study).

What this means for you: if your urine repeatedly shows squamous cells and you have a history of chronic bladder infections, catheter use, or bladder stones, the cells may not be simple contamination. Chronically infected bladders show squamous metaplasia in 86% to 92% of cases. A conversation with a urologist about whether cystoscopy or ongoing monitoring is appropriate would be worthwhile, especially if atypical cells have been identified.

Questions This Biomarker Can Answer

• Was my urine sample collected cleanly enough for the results to be trustworthy?
• Could my urinalysis results be giving a false signal for infection because of contamination?
• Are there abnormal squamous cells in my urine that might indicate a bladder or cervical problem?
• Is my chronic bladder irritation causing tissue changes that need monitoring?
• Do I need to recollect my sample using a cleaner technique before my doctor and I make treatment decisions?