From the Guidelines
The presence of more than 10 squamous epithelial cells in a urinalysis indicates sample contamination. This is based on the evidence from the Annals of Emergency Medicine 1, which suggests that a urine sample with a significant number of epithelial cells must be considered contaminated.
Key Points to Consider
- The study highlights the importance of proper collection techniques, such as clean-catch or catheterization, to minimize contamination rates 1.
- Contamination rates for clean-catch urine samples can range from 0% to 29%, emphasizing the need for careful collection methods 1.
- The presence of squamous epithelial cells in small numbers is considered normal, but excessive numbers suggest contamination with cells from the urethra, vagina, or external genitalia.
Clinical Implications
- If contamination is suspected, a clean-catch midstream technique should be used for recollection, with proper cleansing of the genital area before sampling.
- In critical situations, catheterization or suprapubic aspiration might be considered to obtain an uncontaminated specimen, given their higher sensitivity and specificity 1.
Important Considerations for Clinical Practice
- Clinicians should be aware of the potential for contamination and take steps to minimize it, such as using proper collection techniques and considering the patient's clinical context.
- The threshold of more than 10 squamous epithelial cells per high-power field (HPF) can serve as a guideline for identifying contaminated samples, but clinical judgment and consideration of individual patient factors are also crucial.
From the Research
Threshold of Squamous Epithelial Cells
- The threshold of squamous epithelial cells in a urinalysis that indicates sample contamination is not universally defined, but several studies provide insights:
- A study published in 2022 2 found that having fewer than 2 squamous epithelial cells per high power field increased the positive predictive value of referral urinalyses for true microscopic hematuria.
- Another study from 2025 3 established cutoffs for squamous epithelial cells (SEC) as 21.35 SEC/µL for women and 5.05 SEC/µL for men to identify sample contamination or colonization scenarios.
- A 2016 study 4 found that the presence of more than 8 SECs/low-powered field (lpf) was associated with poor predictive performance of traditional urinalysis measures, but did not provide a clear threshold for contamination.
Variability in Thresholds
- Different studies suggest varying thresholds for squamous epithelial cells to indicate sample contamination, highlighting the need for further research to establish a standardized threshold.
- The 2022 study 2 used a threshold of 2 squamous epithelial cells per high power field, while the 2025 study 3 used cutoffs of 21.35 SEC/µL for women and 5.05 SEC/µL for men.
- The 2016 study 4 found that more than 8 SECs/lpf was associated with poor predictive performance, but did not provide a clear threshold for contamination.
Limitations and Considerations
- The presence of squamous epithelial cells is not a definitive indicator of sample contamination, as it can also be present in properly collected samples 5.
- The threshold for squamous epithelial cells may vary depending on the population being studied, the collection method, and the laboratory techniques used 6, 4, 3.