ASCP Tissue Fixation and Decalcification 2

Question 1

Which fixative type is most likely to mask antigenic epitopes, necessitating antigen retrieval before immunohistochemistry?

Accepted Answer

10% neutral buffered formalin

Answer

Formalin cross-links proteins and masks antigenic epitopes; heat-induced or proteolytic antigen retrieval must be performed to unmask these epitopes before IHC staining.

Question 2

Zenker's fixative contains which hazardous heavy metal component?

Accepted Answer

Mercuric chloride

Answer

Zenker's fixative contains mercuric chloride, which is highly toxic and requires special handling and disposal procedures, contributing to its decline in modern laboratories.

Question 3

Which fixative is preferred when preservation of glycogen in tissue is the primary concern?

Accepted Answer

Absolute alcohol (ethanol)

Answer

Absolute alcohol preserves glycogen by precipitating surrounding proteins through dehydration without dissolving the water-soluble glycogen molecules.

Question 4

What is the ideal pH range for neutral buffered formalin to prevent artifact formation?

Accepted Answer

6.8–7.4

Answer

NBF should be maintained between pH 6.8 and 7.4 to prevent the formation of formalin pigment (acid formaldehyde hematin) and optimize tissue preservation.

Question 5

What is formalin pigment and how is it prevented?

Accepted Answer

A brown artifact from acidic formalin reacting with hemoglobin; prevented by using buffered formalin

Answer

Formalin pigment (acid formaldehyde hematin) is a brown refractile artifact that forms when acidic, unbuffered formalin reacts with hemoglobin in bloody tissue; buffering the formalin to neutral pH prevents its formation.

ASCP - Histotechnician Test Practice Test

ASCP - Histotechnician Test Practice Test

ASCP Tissue Fixation and Decalcification 2