ASCP Tissue Fixation and Decalcification

Question 1

What is the primary purpose of tissue fixation in histology?

Accepted Answer

To prevent autolysis and putrefaction

Answer

Fixation prevents autolysis (self-digestion by intracellular enzymes) and putrefaction (bacterial decomposition) by stabilizing tissue proteins and halting enzymatic activity.

Question 2

Which fixative is considered the standard routine fixative used in most histopathology laboratories?

Accepted Answer

10% neutral buffered formalin

Answer

10% neutral buffered formalin (NBF) is the universal standard fixative because it preserves tissue morphology well and is compatible with most staining and molecular applications.

Question 3

What is the approximate formaldehyde concentration in a solution labeled '10% neutral buffered formalin'?

Accepted Answer

3.7–4% formaldehyde

Answer

10% formalin is a 1:10 dilution of the 37–40% formaldehyde stock solution, yielding an actual formaldehyde concentration of approximately 3.7–4%.

Question 4

What is the primary chemical mechanism by which formalin fixes tissue?

Accepted Answer

Formation of methylene bridges that cross-link proteins

Answer

Formalin reacts with amino groups of proteins to form methylene bridges, creating a stable cross-linked protein network that preserves tissue architecture.

Question 5

Bouin's fixative is particularly well-suited for which type of tissue specimen?

Accepted Answer

Testicular and gastrointestinal biopsies

Answer

Bouin's fixative (picric acid, formalin, glacial acetic acid) provides excellent cytological detail, especially for testicular and gastrointestinal biopsies.

ASCP - Histotechnician Test Practice Test

ASCP - Histotechnician Test Practice Test

ASCP Tissue Fixation and Decalcification