If bacteria are detected in a specimen, which finding suggests bacteria were introduced during collection rather than from a urinary tract infection?

• A. Positive nitrite
• B. Squamous epithelial cells present
• C. Transitional cells present
• D. Renal epithelial cells present

Answer: (B)

When bacteria appear in a urine specimen, the key is to assess the collection quality. Squamous epithelial cells come from the skin and the distal urethra/vagina; finding them in large numbers suggests the sample was contaminated during collection with vaginal or skin flora. That contamination can bring bacteria into the specimen without them reflecting a true urinary tract infection.

Positive nitrite points to bacteria that are actually present in the urinary tract and capable of reducing nitrates, which supports a real infection rather than contamination. Transitional and renal epithelial cells can be seen with irritation or infection of the urinary tract or kidneys, but they don’t specifically indicate a specimen collected from contamination.

So, the presence of squamous epithelial cells is the best clue that bacteria were introduced during collection rather than originating from a urinary tract infection.