American Society for Clinical Pathology (ASCP) Histotechnologist Practice Test

What are the three main processes involved in tissue processing?

1. Fixation, staining, and clearing

2. Dehydration, clearing, and infiltration

3. Embedding, slicing, and staining

4. Transporting, freezing, and fixing

The correct answer is: Dehydration, clearing, and infiltration

The three main processes involved in tissue processing are dehydration, clearing, and infiltration, which are crucial steps in preparing biological tissues for microscopic examination. Dehydration is the first step, where water is removed from the tissue specimens using ascending concentrations of alcohol. This is essential because most embedding mediums, such as paraffin wax, are not miscible with water, necessitating the removal of water to prevent poor infiltration. Following dehydration, the second step is clearing. In this phase, the tissue specimen is treated with a clearing agent (often xylene or toluene) that replaces the alcohol. The purpose of clearing is to make the tissue transparent and allow the embedding medium (paraffin wax) to infiltrate effectively. The clearing agent removes the remaining alcohol and prepares the sample for the infiltration step. The final step is infiltration, where the cleared and dehydrated tissue is immersed in molten paraffin wax or another embedding medium. This step allows the embedding medium to penetrate the tissue completely, filling the spaces within the tissue structure. It is a critical phase because it provides the support needed when the specimen is later sliced into thin sections for microscopic examination. Understanding these processes is vital since they directly affect the quality of tissue samples and the accuracy of microscopic evaluations.