Canadian Society for Medical Laboratory Science (CSMLS) Practice Exam

When is xylene used in laboratory procedures?

1. Fixation of autopsy material

2. Clearing of tissue

3. Attaching cover slips to slides

4. Dehydration of tissue

The correct answer is: Dehydration of tissue

Xylene plays a crucial role in laboratory procedures, particularly in the processing of tissue specimens for histopathology. It is a solvent that is mainly used for the clearing of tissue. This step occurs after dehydration, where tissues that have been processed through a series of alcohol baths to remove water are then treated with xylene to clear any remaining alcohol and prepare the tissue for infiltration with paraffin wax. During the clearing process, xylene effectively removes the alcohol from the tissue, allowing the infiltration of wax to take place. It is essential for ensuring that the tissue retains its morphology and is properly supported during sectioning for microscopic examination. Therefore, its primary function within these processes is not in dehydration but rather in facilitating the transition from dehydration to embedding. The other choices involve steps that are not directly associated with the use of xylene. For instance, while fixation is critical for preserving tissue structure, it typically involves formalin or other fixatives rather than xylene. Attaching cover slips to slides is generally done using a mounting medium that isn't xylene, and dehydration is the step that precedes clearing, with other dehydrating agents being used prior to this process.