From the Guidelines
In a urinalysis (UA), fewer than 10 squamous epithelial cells per low-power field is considered acceptable, while more than this may indicate contamination. This threshold is based on the quality of the sample and its potential to reflect the true condition of the urinary tract. When considering the quality of a urine sample, it's essential to look at the presence of squamous epithelial cells as an indicator of contamination, as noted in studies discussing the proper collection and examination of sputum samples, which also apply to urine samples in terms of contamination assessment 1. Key points to consider in assessing contamination include:
- The presence of squamous epithelial cells, which are typically found on the skin and can indicate contamination during sample collection.
- The importance of proper sample collection technique to minimize contamination, such as using a mid-stream clean-catch method for urine samples.
- The need for a repeat sample if contamination is suspected, to ensure accurate results for diagnosis and treatment decisions. In clinical practice, the goal is to obtain a sample that accurately reflects the condition of the urinary tract, and thus, minimizing contamination is crucial. Proper collection and handling of the sample are critical to achieving this goal and ensuring that any findings are reliable and useful for guiding patient care.
From the Research
Squamous Cells and Urine Contamination
- The presence of squamous epithelial cells (SECs) in urine samples has been studied as a potential indicator of contamination, but the evidence is mixed 2, 3, 4, 5, 6.
- A study from 2016 found that SEC count was a poor predictor of urine culture contamination, with an area under the ROC curve of 0.680 2.
- Another study from 1998 found that the presence of squamous cells in urine samples did not accurately predict bacterial contamination, with a predictive value of 21% 3.
- A 2020 study found that the presence of SECs reduced the accuracy of urinalysis for predicting positive urine cultures, with individual urinalysis markers having lower area under the curve (AUC) values in contaminated samples 5.
- A 2025 study established cutoffs for SECs to discriminate between contaminated and non-contaminated urine samples, with values of 21.35 SEC/µL for women and 5.05 SEC/µL for men 4.
- However, a 2021 study found no correlation between epithelial cells and contamination, suggesting that SECs may not be a reliable indicator of contamination 6.
Cutoff Values for Squamous Cells
- A study from 2025 established cutoffs for SECs to discriminate between contaminated and non-contaminated urine samples, with values of:
- 21.35 SEC/µL for women
- 5.05 SEC/µL for men 4
- Another study from 2016 found that samples with more than 8 SECs/low-powered field (lpf) had a lower positive likelihood ratio for predicting bacteriuria via urinalysis 2.