DC HISTOTECHNOLOGIST LICENSURE EXAM 2026/2027 | 150 VERIFIED
QUESTIONS & ANSWERS | DC HEALTH CLINICAL LABORATORY SCIENCE PREP |
INSTANT DOWNLOAD
SECTION 1: FIXATION (Questions 1–30)
1. Which fixative is considered the standard of choice for routine histology and immunohistochemistry
because it provides excellent morphological preservation through cross-linking proteins?
A. Bouin's solution
B. 10% Neutral Buffered Formalin (NBF)
C. Zenker's fixative
D. Carnoy's solution
Answer: B
Rationale: 10% Neutral Buffered Formalin (NBF) is an aldehyde fixative that cross-links proteins,
providing excellent preservation of cellular morphology. Its buffered nature (pH ~7.0-7.4) prevents the
formation of formalin pigment and preserves antigenicity for most immunohistochemical stains. Bouin's,
Zenker's, and Carnoy's are non-routine fixatives used for specific purposes and require different
processing protocols.
2. A tissue sample is placed in formalin that has been sitting in a plastic container exposed to sunlight
for several weeks. The solution has turned cloudy and acidic. What is the most likely consequence for
tissue fixed in this solution?
A. Enhanced staining of nuclei.
B. Formation of formalin pigment (acid hematin) artifact.
C. Improved preservation of enzyme activity.
D. Faster penetration of the fixative.
Answer: B
Rationale: Prolonged exposure to sunlight and air causes formalin to oxidize to formic acid, lowering
the pH. When acidic formalin reacts with hemoglobin in tissues, it forms acid hematin, a brown-black
pigment artifact. Properly buffered NBF prevents this by maintaining a neutral pH.
3. What is the recommended ratio of fixative volume to tissue volume for optimal fixation?
A. 1:1
B. 5:1
,C. 10:1
D. 20:1
Answer: C
Rationale: A minimum volume ratio of 10:1 (fixative to tissue) is recommended to ensure an adequate
supply of fixative molecules for cross-linking and to prevent the buildup of metabolic wastes and
dilution of the fixative by tissue fluids. A lower ratio can lead to incomplete fixation.
4. Which factor most significantly affects the rate of fixation?
A. The color of the tissue container.
B. The temperature of the fixative.
C. The type of cassette used.
D. The age of the patient.
Answer: B
Rationale: The rate of chemical reactions, including fixation, increases with temperature. Heating
formalin (e.g., to 37–40°C) accelerates cross-linking and reduces fixation time. However, higher
temperatures can also increase tissue shrinkage and autolysis if not carefully controlled.
5. A tissue biopsy is received in the laboratory in a container with no fixative. What is the most critical
immediate action?
A. Place the specimen in a freezer.
B. Add 10% NBF as soon as possible.
C. Allow the tissue to air dry.
D. Place the specimen in saline.
Answer: B
Rationale: The most critical step is to immerse the tissue in an appropriate fixative (10% NBF) as soon
as possible to prevent autolysis and putrefaction, which rapidly degrade cellular morphology. Freezing
without proper preparation causes ice crystal artifacts, and air drying or saline are not fixatives.
6. What is the purpose of adding a buffer (e.g., phosphate) to a formalin solution?
A. To increase the penetration rate of the fixative.
B. To maintain a stable pH and prevent the formation of acid hematin pigment.
C. To enhance the cross-linking of proteins.
D. To dissolve lipids in the tissue.
Answer: B
Rationale: Buffers such as phosphate maintain the pH of the formalin solution near neutrality (pH 7.0-
,7.4). This prevents the oxidation of formalin to formic acid and the subsequent formation of acid
hematin pigment, which can obscure tissue detail.
7. Which fixative is a picric acid-based solution that requires removal (e.g., through alcohol washes) to
prevent interference with certain staining procedures?
A. 10% NBF
B. Bouin's solution
C. Glutaraldehyde
D. Osmium tetroxide
Answer: B
Rationale: Bouin's solution contains picric acid, which can impart a yellow color to tissues and interfere
with certain stains (e.g., trichrome stains). Picric acid must be removed from the tissue through washing
in alcohol (usually 70% ethanol) before further processing.
8. A tissue sample is fixed in formalin for 48 hours. The pathologist reports that the tissue is "over-
fixed" and difficult to section. What is a potential consequence of over-fixation?
A. The tissue becomes excessively hard and brittle, leading to sectioning artifacts.
B. The tissue becomes too soft and mushy.
C. The tissue loses its antigenicity for all stains.
D. The tissue undergoes autolysis.
Answer: A
Rationale: Over-fixation in formalin can cause excessive cross-linking, making the tissue hard and
brittle. This can lead to difficulty in sectioning, resulting in cracks, chatter, and uneven sections. It may
also mask antigenic sites, but the primary physical consequence is hardening.
9. Which fixative is primarily used for electron microscopy because it preserves ultrastructural detail
better than formalin?
A. 10% NBF
B. Glutaraldehyde
C. Bouin's solution
D. B-5 fixative
Answer: B
Rationale: Glutaraldehyde is a dialdehyde that cross-links proteins more extensively than
formaldehyde, providing superior preservation of cellular ultrastructure (e.g., organelles, membranes)
for electron microscopy. It penetrates tissue more slowly than formalin.
, 10. What is the purpose of "fixation" in the context of histology?
A. To stain tissue for visualization.
B. To preserve tissue morphology and prevent autolysis and putrefaction.
C. To embed tissue in paraffin.
D. To cut tissue into thin sections.
Answer: B
Rationale: Fixation is the first and most critical step in tissue processing. Its primary goal is to preserve
the structural integrity of cells and tissues by halting autolysis (self-digestion) and putrefaction (bacterial
decomposition), while also hardening the tissue for subsequent processing.
11. A tissue sample is fixed in a solution containing mercuric chloride (e.g., B-5 fixative). What special
handling is required after fixation?
A. The tissue must be washed in water.
B. The mercury pigment must be removed (e.g., with iodine) before staining.
C. The tissue must be frozen immediately.
D. No special handling is required.
Answer: B
Rationale: Mercuric chloride fixatives (e.g., B-5, Zenker's) leave behind a brown-black mercury pigment
in the tissue. This pigment must be removed (de-zenkerized) before staining, typically using a dilute
iodine solution followed by sodium thiosulfate, to prevent interference with the stain.
12. What is the effect of a hypertonic fixative solution on tissue?
A. The tissue swells.
B. The tissue shrinks.
C. The tissue remains unchanged.
D. The tissue dissolves.
Answer: B
Rationale: A hypertonic solution has a higher solute concentration than the cell cytoplasm. Water
moves out of the cells by osmosis, causing the tissue to shrink and creating shrinkage artifacts. Isotonic
or slightly hypertonic fixatives are preferred to minimize this effect.
13. Which of the following is a precipitating fixative that preserves nucleic acids but causes significant
tissue shrinkage?
A. Formalin
B. Glutaraldehyde
QUESTIONS & ANSWERS | DC HEALTH CLINICAL LABORATORY SCIENCE PREP |
INSTANT DOWNLOAD
SECTION 1: FIXATION (Questions 1–30)
1. Which fixative is considered the standard of choice for routine histology and immunohistochemistry
because it provides excellent morphological preservation through cross-linking proteins?
A. Bouin's solution
B. 10% Neutral Buffered Formalin (NBF)
C. Zenker's fixative
D. Carnoy's solution
Answer: B
Rationale: 10% Neutral Buffered Formalin (NBF) is an aldehyde fixative that cross-links proteins,
providing excellent preservation of cellular morphology. Its buffered nature (pH ~7.0-7.4) prevents the
formation of formalin pigment and preserves antigenicity for most immunohistochemical stains. Bouin's,
Zenker's, and Carnoy's are non-routine fixatives used for specific purposes and require different
processing protocols.
2. A tissue sample is placed in formalin that has been sitting in a plastic container exposed to sunlight
for several weeks. The solution has turned cloudy and acidic. What is the most likely consequence for
tissue fixed in this solution?
A. Enhanced staining of nuclei.
B. Formation of formalin pigment (acid hematin) artifact.
C. Improved preservation of enzyme activity.
D. Faster penetration of the fixative.
Answer: B
Rationale: Prolonged exposure to sunlight and air causes formalin to oxidize to formic acid, lowering
the pH. When acidic formalin reacts with hemoglobin in tissues, it forms acid hematin, a brown-black
pigment artifact. Properly buffered NBF prevents this by maintaining a neutral pH.
3. What is the recommended ratio of fixative volume to tissue volume for optimal fixation?
A. 1:1
B. 5:1
,C. 10:1
D. 20:1
Answer: C
Rationale: A minimum volume ratio of 10:1 (fixative to tissue) is recommended to ensure an adequate
supply of fixative molecules for cross-linking and to prevent the buildup of metabolic wastes and
dilution of the fixative by tissue fluids. A lower ratio can lead to incomplete fixation.
4. Which factor most significantly affects the rate of fixation?
A. The color of the tissue container.
B. The temperature of the fixative.
C. The type of cassette used.
D. The age of the patient.
Answer: B
Rationale: The rate of chemical reactions, including fixation, increases with temperature. Heating
formalin (e.g., to 37–40°C) accelerates cross-linking and reduces fixation time. However, higher
temperatures can also increase tissue shrinkage and autolysis if not carefully controlled.
5. A tissue biopsy is received in the laboratory in a container with no fixative. What is the most critical
immediate action?
A. Place the specimen in a freezer.
B. Add 10% NBF as soon as possible.
C. Allow the tissue to air dry.
D. Place the specimen in saline.
Answer: B
Rationale: The most critical step is to immerse the tissue in an appropriate fixative (10% NBF) as soon
as possible to prevent autolysis and putrefaction, which rapidly degrade cellular morphology. Freezing
without proper preparation causes ice crystal artifacts, and air drying or saline are not fixatives.
6. What is the purpose of adding a buffer (e.g., phosphate) to a formalin solution?
A. To increase the penetration rate of the fixative.
B. To maintain a stable pH and prevent the formation of acid hematin pigment.
C. To enhance the cross-linking of proteins.
D. To dissolve lipids in the tissue.
Answer: B
Rationale: Buffers such as phosphate maintain the pH of the formalin solution near neutrality (pH 7.0-
,7.4). This prevents the oxidation of formalin to formic acid and the subsequent formation of acid
hematin pigment, which can obscure tissue detail.
7. Which fixative is a picric acid-based solution that requires removal (e.g., through alcohol washes) to
prevent interference with certain staining procedures?
A. 10% NBF
B. Bouin's solution
C. Glutaraldehyde
D. Osmium tetroxide
Answer: B
Rationale: Bouin's solution contains picric acid, which can impart a yellow color to tissues and interfere
with certain stains (e.g., trichrome stains). Picric acid must be removed from the tissue through washing
in alcohol (usually 70% ethanol) before further processing.
8. A tissue sample is fixed in formalin for 48 hours. The pathologist reports that the tissue is "over-
fixed" and difficult to section. What is a potential consequence of over-fixation?
A. The tissue becomes excessively hard and brittle, leading to sectioning artifacts.
B. The tissue becomes too soft and mushy.
C. The tissue loses its antigenicity for all stains.
D. The tissue undergoes autolysis.
Answer: A
Rationale: Over-fixation in formalin can cause excessive cross-linking, making the tissue hard and
brittle. This can lead to difficulty in sectioning, resulting in cracks, chatter, and uneven sections. It may
also mask antigenic sites, but the primary physical consequence is hardening.
9. Which fixative is primarily used for electron microscopy because it preserves ultrastructural detail
better than formalin?
A. 10% NBF
B. Glutaraldehyde
C. Bouin's solution
D. B-5 fixative
Answer: B
Rationale: Glutaraldehyde is a dialdehyde that cross-links proteins more extensively than
formaldehyde, providing superior preservation of cellular ultrastructure (e.g., organelles, membranes)
for electron microscopy. It penetrates tissue more slowly than formalin.
, 10. What is the purpose of "fixation" in the context of histology?
A. To stain tissue for visualization.
B. To preserve tissue morphology and prevent autolysis and putrefaction.
C. To embed tissue in paraffin.
D. To cut tissue into thin sections.
Answer: B
Rationale: Fixation is the first and most critical step in tissue processing. Its primary goal is to preserve
the structural integrity of cells and tissues by halting autolysis (self-digestion) and putrefaction (bacterial
decomposition), while also hardening the tissue for subsequent processing.
11. A tissue sample is fixed in a solution containing mercuric chloride (e.g., B-5 fixative). What special
handling is required after fixation?
A. The tissue must be washed in water.
B. The mercury pigment must be removed (e.g., with iodine) before staining.
C. The tissue must be frozen immediately.
D. No special handling is required.
Answer: B
Rationale: Mercuric chloride fixatives (e.g., B-5, Zenker's) leave behind a brown-black mercury pigment
in the tissue. This pigment must be removed (de-zenkerized) before staining, typically using a dilute
iodine solution followed by sodium thiosulfate, to prevent interference with the stain.
12. What is the effect of a hypertonic fixative solution on tissue?
A. The tissue swells.
B. The tissue shrinks.
C. The tissue remains unchanged.
D. The tissue dissolves.
Answer: B
Rationale: A hypertonic solution has a higher solute concentration than the cell cytoplasm. Water
moves out of the cells by osmosis, causing the tissue to shrink and creating shrinkage artifacts. Isotonic
or slightly hypertonic fixatives are preferred to minimize this effect.
13. Which of the following is a precipitating fixative that preserves nucleic acids but causes significant
tissue shrinkage?
A. Formalin
B. Glutaraldehyde
