American Society for Clinical Pathology (ASCP) Histotechnologist Practice Test

What has zinc salts replaced in the B-5 solution?

1. Formaldehyde

2. Glyoxal

3. Acetic Acid

4. EDTA

The correct answer is: Formaldehyde

Zinc salts have replaced formaldehyde in the B-5 solution primarily due to their ability to provide better morphological preservation and to enhance the staining quality of tissues, especially in the context of cytological and histological preparations. The B-5 fixative, which is a buffered formalin solution that contains zinc salts, is notably effective in preserving cellular detail by stabilizing proteins and cellular structures more effectively than formaldehyde alone. The use of zinc salts minimizes formalin's tendency to produce artifacts and allows for a reduction in background staining, which is particularly advantageous when preparing delicate tissues or when exact morphological identification is crucial. This improvement in fixation leads to better immunohistochemical staining outcomes and aids pathologists in making accurate diagnoses. When considering other components such as glyoxal, acetic acid, or EDTA, these substances serve different purposes in tissue preparation. Glyoxal is another type of fixative that can be used in alternative tissue processes but does not have the same buffering effects combined with zinc. Acetic acid generally serves to precipitate nucleic acids away from proteins, and EDTA is primarily used as a chelating agent for metal ions, neither of which replace formaldehyde in the B-5 solution. Thus, zinc