Canadian Society for Medical Laboratory Science (CSMLS) Practice Exam

Which step is out of order for histological processing?

1. Gross examination

2. Decalcification

3. Fixation

4. Dehydration

The correct answer is: Decalcification

The process of histological processing involves a series of steps that are essential for preparing tissue samples for microscopic examination. In a typical histology workflow, the first step is fixation, which preserves the tissue structure by preventing degradation and autolysis. Following fixation, the samples undergo a gross examination to assess the condition of the tissue and plan for further processing. Decalcification is a necessary procedure for samples containing bone or calcified tissue, which typically occurs before dehydration. Dehydration is the next step that removes water from the tissue, preparing it for infiltration with paraffin or embedding media. Therefore, decalcification should happen prior to dehydration when calcified tissues are involved. Thus, placing decalcification in an incorrect sequence in the processing workflow disrupts the logical order necessary for effective histological preparation, making it the out-of-order step in this list.