Vaginal contamination in urine specimens may cause the appearance of which of the following?

The presence of squamous epithelial cells in urine specimens is indicative of vaginal contamination. These cells are part of the vaginal lining and are frequently sloughed off into urine, especially in females. When a urine sample is collected, if there is contamination from the vaginal area, these cells can appear in the specimen, potentially leading to a misinterpretation of the urinary condition.

It's important to understand that the other options do not typically result from vaginal contamination. Oval fat bodies are associated with lipiduria, often seen in nephrotic syndrome, and are not linked to contamination. Amorphous crystals, while they can be found in urine, do not correlate with contamination but rather with the crystallization of certain substances in the urine depending on the pH and concentration. Hyaline casts are indicative of renal conditions and are not a result of contamination from the vaginal area. Thus, the presence of squamous epithelial cells is the most relevant indication of vaginal contamination in urine specimens.