2026 QIHC Exam Prep: Immunohistochemistry
Qualification Practice Questions, Answer Rationales,
Immunostaining, Antibodies, Tissue Analysis, Quality
Control & Diagnostic Pathology Study Guide
SECTION 1: GENERAL IMMUNOLOGY (Questions 1–12)
1. A technologist is comparing monoclonal and polyclonal antibodies for an IHC
assay. Which of the following best describes a key advantage of monoclonal
antibodies over polyclonal antibodies?
A) Monoclonal antibodies recognize multiple epitopes on the same antigen
B) Monoclonal antibodies are highly specific for a single epitope, reducing
cross-reactivity
C) Monoclonal antibodies are less expensive to produce
D) Monoclonal antibodies are more tolerant of fixation variability
Rationale: Monoclonal antibodies are produced from a single B-cell clone and
recognize a single epitope, providing high specificity and consistent, reproducible
staining. Polyclonal antibodies recognize multiple epitopes and are more tolerant
of fixation variability but are more prone to cross-reactivity. Monoclonal
antibodies are generally more expensive to produce. The General Immunology
domain comprises 5–10% of the QIHC exam .
2. A polyclonal antibody is produced by immunizing a host animal with an antigen.
Which of the following is a characteristic of polyclonal antibodies?
A) They are produced by hybridoma technology
B) They recognize multiple epitopes and may have greater sensitivity due to
signal amplification from multiple antibodies binding the same antigen
C) They are identical in every batch produced
D) They are the preferred choice for highly specific nuclear markers
Rationale: Polyclonal antibodies are produced by multiple B-cell clones and
recognize multiple epitopes on the same antigen. This can provide greater
sensitivity because multiple antibodies bind the target, amplifying the signal.
,However, they show batch-to-batch variability and are more prone to cross-
reactivity. Hybridoma technology is used for monoclonal antibodies.
3. An antibody is composed of two heavy chains and two light chains. Which
region of the antibody is responsible for antigen binding?
A) The Fc region
B) The variable region (Fab) of the heavy and light chains
C) The constant region of the heavy chain
D) The hinge region
Rationale: The Fab (fragment antigen-binding) region contains the variable
domains of both heavy and light chains, which form the antigen-binding site. The
Fc (fragment crystallizable) region mediates effector functions and is used for
detection in secondary antibodies. The constant region is conserved and does not
bind antigen.
4. Which immunoglobulin class is most commonly used in IHC as a primary
antibody?
A) IgA
B) IgM
C) IgG
D) IgE
Rationale: IgG is the most commonly used immunoglobulin class for primary
antibodies in IHC. IgG antibodies are stable, easily purified, and can be produced
in large quantities. IgM antibodies are larger and less commonly used. IgA and IgE
are not routinely used in diagnostic IHC.
5. A technologist is selecting a secondary antibody for a primary antibody raised in
rabbit. The secondary antibody should be:
A) Anti-rabbit raised in mouse
B) Anti-rabbit raised in goat and conjugated to an enzyme
C) Anti-mouse raised in rabbit
D) Anti-human raised in goat
,Rationale: The secondary antibody must be directed against the species in which
the primary antibody was raised. For a rabbit primary antibody, the secondary
should be anti-rabbit (e.g., raised in goat). The secondary is typically conjugated to
an enzyme (HRP or AP) for detection. Using an anti-mouse secondary would not
bind the rabbit primary.
6. What is the primary function of the Fc region of an antibody?
A) Antigen binding
B) Mediating effector functions and providing a site for secondary antibody
binding
C) Forming the hinge region
D) Determining antibody class
Rationale: The Fc region is the constant region of the heavy chain. It mediates
effector functions (e.g., complement activation, Fc receptor binding) and provides
the binding site for secondary antibodies in IHC. The Fab region is responsible for
antigen binding. The hinge region provides flexibility.
7. A technologist is performing a direct IHC stain. Which of the following best
describes this method?
A) The primary antibody is conjugated directly to a label
B) The primary antibody is unconjugated and detected by a secondary
antibody
C) The primary antibody is detected by an avidin-biotin complex
D) The primary antibody is detected by a polymer system
Rationale: Direct IHC involves a primary antibody that is directly conjugated to a
label (e.g., fluorophore or enzyme). It is a one-step method with less sensitivity
than indirect methods. Indirect IHC uses an unconjugated primary antibody
detected by a labeled secondary antibody. The QIHC outline lists direct and
indirect staining under Staining principles .
8. Which of the following is an advantage of indirect IHC over direct IHC?
, A) Fewer steps
B) Signal amplification because multiple secondary antibodies can bind each
primary antibody
C) Less background
D) No need for a secondary antibody
Rationale: Indirect IHC provides signal amplification because multiple secondary
antibodies can bind to a single primary antibody, increasing sensitivity. Direct IHC
is a one-step method with lower sensitivity. Indirect methods require more steps
and may have higher background if not properly controlled. The QIHC outline
includes direct and indirect staining methods.
9. A technologist is evaluating an antibody's specificity. What does the term
"cross-reactivity" refer to?
A) The antibody's ability to bind multiple epitopes on the target antigen
B) The antibody binding to antigens other than the intended target
C) The antibody's affinity for the Fc receptor
D) The antibody's class switching
Rationale: Cross-reactivity refers to an antibody binding to antigens other than its
intended target, leading to false-positive staining. It is a common concern with
polyclonal antibodies. Monoclonal antibodies have higher specificity and reduced
cross-reactivity. Antibody validation must include testing for cross-reactivity.
10. Which of the following best describes the "antigen-antibody lock and key"
model?
A) The antibody undergoes conformational change to bind antigen
B) The antigen-binding site of the antibody is complementary in shape and
chemistry to the epitope of the antigen
C) The antigen binds to the Fc region of the antibody
D) The antibody binds antigen non-specifically through hydrophobic interactions
Rationale: The lock and key model describes the complementary fit between the
antibody's antigen-binding site (paratope) and the antigen's epitope. This
complementary shape and chemistry determine specificity. The Fc region does not
bind antigen. Non-specific binding is not the basis of the lock and key model.
Qualification Practice Questions, Answer Rationales,
Immunostaining, Antibodies, Tissue Analysis, Quality
Control & Diagnostic Pathology Study Guide
SECTION 1: GENERAL IMMUNOLOGY (Questions 1–12)
1. A technologist is comparing monoclonal and polyclonal antibodies for an IHC
assay. Which of the following best describes a key advantage of monoclonal
antibodies over polyclonal antibodies?
A) Monoclonal antibodies recognize multiple epitopes on the same antigen
B) Monoclonal antibodies are highly specific for a single epitope, reducing
cross-reactivity
C) Monoclonal antibodies are less expensive to produce
D) Monoclonal antibodies are more tolerant of fixation variability
Rationale: Monoclonal antibodies are produced from a single B-cell clone and
recognize a single epitope, providing high specificity and consistent, reproducible
staining. Polyclonal antibodies recognize multiple epitopes and are more tolerant
of fixation variability but are more prone to cross-reactivity. Monoclonal
antibodies are generally more expensive to produce. The General Immunology
domain comprises 5–10% of the QIHC exam .
2. A polyclonal antibody is produced by immunizing a host animal with an antigen.
Which of the following is a characteristic of polyclonal antibodies?
A) They are produced by hybridoma technology
B) They recognize multiple epitopes and may have greater sensitivity due to
signal amplification from multiple antibodies binding the same antigen
C) They are identical in every batch produced
D) They are the preferred choice for highly specific nuclear markers
Rationale: Polyclonal antibodies are produced by multiple B-cell clones and
recognize multiple epitopes on the same antigen. This can provide greater
sensitivity because multiple antibodies bind the target, amplifying the signal.
,However, they show batch-to-batch variability and are more prone to cross-
reactivity. Hybridoma technology is used for monoclonal antibodies.
3. An antibody is composed of two heavy chains and two light chains. Which
region of the antibody is responsible for antigen binding?
A) The Fc region
B) The variable region (Fab) of the heavy and light chains
C) The constant region of the heavy chain
D) The hinge region
Rationale: The Fab (fragment antigen-binding) region contains the variable
domains of both heavy and light chains, which form the antigen-binding site. The
Fc (fragment crystallizable) region mediates effector functions and is used for
detection in secondary antibodies. The constant region is conserved and does not
bind antigen.
4. Which immunoglobulin class is most commonly used in IHC as a primary
antibody?
A) IgA
B) IgM
C) IgG
D) IgE
Rationale: IgG is the most commonly used immunoglobulin class for primary
antibodies in IHC. IgG antibodies are stable, easily purified, and can be produced
in large quantities. IgM antibodies are larger and less commonly used. IgA and IgE
are not routinely used in diagnostic IHC.
5. A technologist is selecting a secondary antibody for a primary antibody raised in
rabbit. The secondary antibody should be:
A) Anti-rabbit raised in mouse
B) Anti-rabbit raised in goat and conjugated to an enzyme
C) Anti-mouse raised in rabbit
D) Anti-human raised in goat
,Rationale: The secondary antibody must be directed against the species in which
the primary antibody was raised. For a rabbit primary antibody, the secondary
should be anti-rabbit (e.g., raised in goat). The secondary is typically conjugated to
an enzyme (HRP or AP) for detection. Using an anti-mouse secondary would not
bind the rabbit primary.
6. What is the primary function of the Fc region of an antibody?
A) Antigen binding
B) Mediating effector functions and providing a site for secondary antibody
binding
C) Forming the hinge region
D) Determining antibody class
Rationale: The Fc region is the constant region of the heavy chain. It mediates
effector functions (e.g., complement activation, Fc receptor binding) and provides
the binding site for secondary antibodies in IHC. The Fab region is responsible for
antigen binding. The hinge region provides flexibility.
7. A technologist is performing a direct IHC stain. Which of the following best
describes this method?
A) The primary antibody is conjugated directly to a label
B) The primary antibody is unconjugated and detected by a secondary
antibody
C) The primary antibody is detected by an avidin-biotin complex
D) The primary antibody is detected by a polymer system
Rationale: Direct IHC involves a primary antibody that is directly conjugated to a
label (e.g., fluorophore or enzyme). It is a one-step method with less sensitivity
than indirect methods. Indirect IHC uses an unconjugated primary antibody
detected by a labeled secondary antibody. The QIHC outline lists direct and
indirect staining under Staining principles .
8. Which of the following is an advantage of indirect IHC over direct IHC?
, A) Fewer steps
B) Signal amplification because multiple secondary antibodies can bind each
primary antibody
C) Less background
D) No need for a secondary antibody
Rationale: Indirect IHC provides signal amplification because multiple secondary
antibodies can bind to a single primary antibody, increasing sensitivity. Direct IHC
is a one-step method with lower sensitivity. Indirect methods require more steps
and may have higher background if not properly controlled. The QIHC outline
includes direct and indirect staining methods.
9. A technologist is evaluating an antibody's specificity. What does the term
"cross-reactivity" refer to?
A) The antibody's ability to bind multiple epitopes on the target antigen
B) The antibody binding to antigens other than the intended target
C) The antibody's affinity for the Fc receptor
D) The antibody's class switching
Rationale: Cross-reactivity refers to an antibody binding to antigens other than its
intended target, leading to false-positive staining. It is a common concern with
polyclonal antibodies. Monoclonal antibodies have higher specificity and reduced
cross-reactivity. Antibody validation must include testing for cross-reactivity.
10. Which of the following best describes the "antigen-antibody lock and key"
model?
A) The antibody undergoes conformational change to bind antigen
B) The antigen-binding site of the antibody is complementary in shape and
chemistry to the epitope of the antigen
C) The antigen binds to the Fc region of the antibody
D) The antibody binds antigen non-specifically through hydrophobic interactions
Rationale: The lock and key model describes the complementary fit between the
antibody's antigen-binding site (paratope) and the antigen's epitope. This
complementary shape and chemistry determine specificity. The Fc region does not
bind antigen. Non-specific binding is not the basis of the lock and key model.
