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ASCP HTL practice questions

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Question 1Fixation

What is the primary purpose of tissue fixation?

  1. Decalcify bone before processing
  2. Remove water to allow paraffin infiltration
  3. Preserve morphology and prevent autolysis Correct answer.
  4. Soften tissue to aid sectioning

Explanation

Fixation stabilizes proteins and other cellular components so that tissue structure is preserved and autolysis and putrefaction are prevented. Softening, dehydration, and decalcification are separate processing steps.

Question 2Fixation

A 10% neutral buffered formalin solution contains approximately what percentage of formaldehyde gas?

  1. 10%
  2. 40%
  3. 0.4%
  4. 4% Correct answer.

Explanation

Saturated formalin is about 40% formaldehyde gas; when diluted to 10% formalin, the final formaldehyde concentration is about 4%. The 10% refers to the formalin stock, not to formaldehyde gas itself.

Question 3Fixation

What is the recommended ratio of fixative volume to tissue volume for routine formalin fixation?

  1. 10:1 Correct answer.
  2. 5:1
  3. 1:1
  4. 20:1

Explanation

A 10:1 ratio of fixative to tissue is standard to ensure adequate preservation and prevent exhaustion of the fixative. Smaller ratios may lead to incomplete fixation.

Question 4Fixation

What is the usual pH range of 10% neutral buffered formalin?

  1. 5.0-6.0
  2. 9.0-10.0
  3. 7.0-7.4 Correct answer.
  4. 3.0-4.0

Explanation

Neutral buffered formalin is buffered near physiologic pH, commonly about 7.0 to 7.4. This minimizes acid-induced artifacts such as formalin pigment.

Question 5Fixation

For a small biopsy about 2-3 mm thick, adequate fixation in 10% neutral buffered formalin is generally achieved in:

  1. 15 minutes
  2. 7 days
  3. 1 hour
  4. 6-12 hours Correct answer.

Explanation

Formalin penetrates tissue at roughly 1 mm per hour, so a thin biopsy usually requires several hours, commonly 6-12 hours, for adequate fixation. Much shorter times risk incomplete fixation, while excessively long fixation can mask antigens.

Question 6Fixation

Which fixative is most appropriate for preserving glycogen in tissue sections?

  1. Glutaraldehyde
  2. 10% neutral buffered formalin
  3. Absolute ethanol Correct answer.
  4. Bouin's solution

Explanation

Alcohol-based fixation precipitates proteins and preserves glycogen, which is water soluble and may be lost with aqueous fixatives. Absolute ethanol is therefore useful when glycogen demonstration is needed.

Question 7Fixation

Delayed fixation of a surgical specimen most directly leads to:

  1. Better nuclear detail
  2. Improved antigen preservation
  3. Increased tissue hardness from fixation
  4. Autolysis and loss of morphology Correct answer.

Explanation

Without timely fixation, endogenous enzymes digest tissue and bacteria cause putrefaction, producing autolysis and loss of cellular detail. Prompt fixation is essential for preserving morphology and antigenicity.

Question 8Fixation

Which procedure avoids chemical fixation by rapidly freezing tissue?

  1. Microwave-assisted fixation
  2. Routine paraffin processing
  3. Cryostat frozen section Correct answer.
  4. Acid decalcification

Explanation

Frozen sectioning uses rapid freezing to harden tissue without chemical fixation, allowing immediate intraoperative evaluation. The other procedures involve chemical processing or decalcification.

Question 9Fixation

Formaldehyde fixes tissue primarily by:

  1. Dissolving nucleic acids
  2. Oxidizing membrane lipids
  3. Precipitating proteins through dehydration
  4. Cross-linking amino groups of proteins Correct answer.

Explanation

Formaldehyde reacts with amino groups, forming methylene bridges that cross-link proteins and stabilize tissue structure. It does not primarily act by dehydration, lipid oxidation, or nucleic acid dissolution.

Question 10Fixation

Why is 10% neutral buffered formalin preferred over unbuffered formalin?

  1. It preserves lipids better
  2. It maintains pH and limits formalin pigment Correct answer.
  3. It penetrates dense tissue more rapidly
  4. It decalcifies bone during the fixation step

Explanation

Buffering keeps formalin near neutral pH, reducing acid-catalyzed formation of formalin pigment and better preserving morphology. Penetration rate is not the main reason for buffering.

Question 11Fixation

Glutaraldehyde is superior to formaldehyde for electron microscopy mainly because it:

  1. Requires no buffer and can be used unbuffered
  2. Dissolves lipids and extracts them from membranes
  3. Penetrates tissue more rapidly than formaldehyde does
  4. Forms stable cross-links preserving fine structure Correct answer.

Explanation

Glutaraldehyde has two aldehyde groups and forms more stable cross-links, giving better preservation of fine structural detail for electron microscopy. It penetrates more slowly than formaldehyde and still requires proper buffering.

Question 12Fixation

Bouin's fixative contains picric acid, formalin, and:

  1. Acetic acid Correct answer.
  2. Mercuric chloride
  3. Potassium dichromate
  4. Osmium tetroxide

Explanation

Bouin's solution is a mixture of picric acid, formalin, and acetic acid. It is a picrate-based fixative that can give good nuclear detail but requires removal of picric acid staining.

Question 13Fixation

Overfixation in formalin can mask antigens; which approach is commonly used to restore immunoreactivity?

  1. Decalcification in acid
  2. Antigen retrieval by heat or enzyme Correct answer.
  3. Staining with hematoxylin and eosin
  4. Prolonged washing in running water

Explanation

Heat-induced or enzymatic antigen retrieval can break formalin cross-links and unmask epitopes, improving immunohistochemical staining. Washing, routine staining, and decalcification do not reliably restore masked antigens.

Question 14Fixation

Which fixative would best preserve glycogen for histochemical demonstration?

  1. Carnoy's solution Correct answer.
  2. 10% neutral buffered formalin
  3. Zenker's solution
  4. Bouin's solution

Explanation

Carnoy's solution is alcohol-based and precipitates glycogen, preventing its loss during aqueous processing. Aqueous formalin and other water-containing fixatives are less effective for glycogen preservation.

Question 15Fixation

Lipids are poorly preserved by aqueous formalin because:

  1. Formalin actively dissolves neutral lipids and phospholipids
  2. Lipids are cross-linked by formaldehyde into stable complexes
  3. Aqueous fixatives do not fix lipids, which processing extracts Correct answer.
  4. Lipids are water soluble and diffuse out of the tissue

Explanation

Aqueous fixatives do not stabilize lipids; during dehydration and clearing, lipid solvents extract them and leave empty spaces. Osmium tetroxide or frozen sections are used when lipid preservation is needed.

Question 16Fixation

Which statement describes paraformaldehyde?

  1. It is an osmium tetroxide solution for EM
  2. It is a solid polymer that yields formaldehyde when dissolved Correct answer.
  3. It is a picric acid-based fixative for biopsies
  4. It is a buffered 10% formalin solution used for routine processing

Explanation

Paraformaldehyde is a solid polymer of formaldehyde that depolymerizes when heated or dissolved to produce a formaldehyde solution. It is not the same as routine buffered formalin, Bouin's fluid, or osmium tetroxide.

Question 17Fixation

For a bone specimen that requires both fixation and decalcification, the usual order is:

  1. Skip fixation and decalcify only
  2. Decalcify, then fix in formalin
  3. Fix in formalin, then decalcify Correct answer.
  4. Decalcify during fixation in formalin

Explanation

Bone should be fixed before decalcification so that cellular morphology is stabilized before acid or chelating agents soften the tissue. Decalcification before fixation can allow autolysis and poor morphology.

Question 18Fixation

The standard primary fixative for transmission electron microscopy is:

  1. Bouin's solution
  2. Absolute ethanol
  3. 10% neutral buffered formalin
  4. Glutaraldehyde Correct answer.

Explanation

Glutaraldehyde is the standard primary fixative for transmission electron microscopy because it preserves fine structural detail through stable protein cross-linking. Formalin alone is inadequate for most EM work.

Question 19Fixation

Formalin pigment is most likely to form when:

  1. Tissue is frozen
  2. Acidic formalin or blood-rich tissue is used Correct answer.
  3. Tissue is fixed in well-buffered neutral formalin
  4. Tissue is fixed in alcohol

Explanation

Formalin pigment, also called acid hematin, forms when formalin becomes acidic, especially in blood-rich tissues. Proper buffering of formalin greatly reduces its formation.

Question 20Fixation

Fixative penetration is slowest through:

  1. Aerated lung tissue
  2. Small intestinal mucosa
  3. Dense collagen or bone Correct answer.
  4. Homogeneous liver parenchyma

Explanation

Dense connective tissue and bone have compact matrices that slow diffusion, so fixation is slower than in soft parenchymal organs. Thick or dense specimens may need longer fixation or thinner slices.

Question 21Fixation

In a large solid tissue block, fixation is often incomplete centrally because:

  1. Central tissue lacks a blood supply
  2. Penetration and cross-linking are slow relative to thickness Correct answer.
  3. Formalin evaporates from the center of the tissue block during fixation
  4. Osmotic pressure draws water outward

Explanation

Formalin penetrates by diffusion and fixes tissue as it advances, so thick blocks may have a fixed periphery and an unfixed center. Slicing tissue thinly and allowing adequate time helps ensure complete fixation.

Question 22Fixation

Which fixative is contraindicated for routine paraffin sections because it hardens tissue and contains mercuric chloride, requiring pigment removal?

  1. Osmium tetroxide
  2. Bouin's fluid
  3. Zenker's fluid Correct answer.
  4. Carnoy's fluid

Explanation

Zenker's fluid contains mercuric chloride, which can leave mercury pigment that must be removed with iodine before staining. It also hardens tissue and is less commonly used in routine paraffin processing today.

Question 23Fixation

Osmium tetroxide is used mainly for electron microscopy because it:

  1. Penetrates tissue more rapidly than formalin does
  2. Preserves glycogen for histochemistry
  3. Fixes and stains lipids, especially membranes Correct answer.
  4. Decalcifies bone

Explanation

Osmium tetroxide reacts with unsaturated lipids, stabilizing and staining membranes so they are visible in electron micrographs. It penetrates poorly and is hazardous, limiting its use to specialized EM work.

Question 24Fixation

Uric acid crystals in tissue are best preserved by fixation in:

  1. Bouin's solution
  2. Glutaraldehyde
  3. Absolute alcohol Correct answer.
  4. 10% neutral buffered formalin

Explanation

Uric acid dissolves in aqueous fixatives, so alcohol fixation is used to preserve uric acid crystals. Aqueous formalin and other water-containing fixatives may allow the crystals to be lost.

Question 25Fixation

Which statement about microwave fixation is correct?

  1. It completely replaces formalin in all routine processing
  2. It decalcifies bone while fixing
  3. It is used only for electron microscopy
  4. It accelerates fixation but needs temperature control Correct answer.

Explanation

Microwave energy can speed fixation by heating tissue and fixative, but uncontrolled heating can create artifacts and uneven fixation. It is an adjunct to, not a complete replacement for, standard formalin fixation.

Question 26Fixation

A laboratory receives a 2 cm³ block of tissue for routine processing. According to standard practice, what is the minimum volume of 10% neutral buffered formalin that should be provided for adequate fixation?

  1. 20 mL Correct answer.
  2. 2 mL
  3. 10 mL
  4. 40 mL

Explanation

The accepted guideline is a fixative-to-tissue volume ratio of at least 10:1, so a 2 cm³ specimen requires roughly 20 mL of formalin. This ratio maintains an adequate concentration gradient so that fixative continues to diffuse into the tissue as it is consumed and diluted by tissue fluids. A container should also not be so full that the specimen is compressed or poorly covered.

Question 27Processing, Embedding, and Microtomy

What section thickness is routinely used for paraffin-embedded tissue stained with hematoxylin and eosin?

  1. 10 to 15 µm
  2. 20 to 25 µm
  3. 4 to 5 µm Correct answer.
  4. 1 to 2 µm

Explanation

Routine light microscopy uses sections of about 4 to 5 µm, thin enough that most cells form a single layer and dyes penetrate evenly, yet thick enough to preserve architecture. Thinner sections are reserved for special techniques such as immunohistochemistry or electron microscopy.

Question 28Processing, Embedding, and Microtomy

Dehydration of routinely fixed tissue is normally begun in which concentration of ethanol?

  1. 50% ethanol
  2. 95% ethanol
  3. 70% ethanol Correct answer.
  4. Absolute isopropanol

Explanation

Graded dehydration starts at about 70% ethanol because moving fixed tissue directly into stronger alcohol causes abrupt osmotic shrinkage and hardening. Concentrations are then raised stepwise to 95% and absolute alcohol.

Question 29Processing, Embedding, and Microtomy

Which reagent is the most widely used clearing agent in routine paraffin processing?

  1. Formalin
  2. Xylene Correct answer.
  3. Acetone
  4. Paraffin

Explanation

Clearing agents must be miscible with both dehydrating alcohol and paraffin; xylene meets this requirement and is the standard routine choice. Acetone and formalin do not serve a clearing role in a paraffin schedule.

Question 30Processing, Embedding, and Microtomy

Routine paraffin embedding medium is selected with a melting point in which range?

  1. 56 to 58 °C Correct answer.
  2. 46 to 50 °C
  3. 30 to 34 °C
  4. 38 to 42 °C

Explanation

Paraffin with a melting point near 56 to 58 °C gives ribbons that are firm enough to cut at room temperature yet soft enough to section without excessive compression. Lower-melting waxes are too soft for routine blocks.

Question 31Processing, Embedding, and Microtomy

What temperature range is recommended for the flotation bath used to spread paraffin sections?

  1. 58 to 62 °C
  2. 40 to 45 °C Correct answer.
  3. Room temperature, about 22 °C
  4. 50 to 55 °C

Explanation

A bath a few degrees below the paraffin melting point, roughly 40 to 45 °C, relaxes the section so wrinkles flatten without melting the wax. Higher temperatures distort and over-expand the tissue.

Question 32Processing, Embedding, and Microtomy

What chamber temperature is typical for routine frozen sectioning in a cryostat?

  1. -20 to -25 °C Correct answer.
  2. -35 to -40 °C
  3. -5 to -10 °C
  4. -50 to -60 °C

Explanation

A cryostat chamber of about -20 to -25 °C keeps the tissue and the supporting medium firm enough to cut 4 to 6 µm sections without shattering. Colder temperatures make tissue brittle and produce chatter.

Question 33Processing, Embedding, and Microtomy

Which microtome type is standard for cutting paraffin blocks in a histology laboratory?

  1. Ultramicrotome
  2. Sliding microtome
  3. Rotary microtome Correct answer.
  4. Base-sledge microtome

Explanation

The rotary microtome advances the block on a screw mechanism and cuts with a vertical flywheel motion, giving reproducible thin sections from paraffin blocks. Sliding and sledge types are used for hard or large specimens, and the ultramicrotome is for electron microscopy.

Question 34Processing, Embedding, and Microtomy

How should a tubular structure such as a vas deferens be embedded to obtain a true cross-section?

  1. On end, perpendicular to the block face Correct answer.
  2. Along its length, parallel to the block face
  3. Lying flat on its side
  4. At a 45-degree tilt to the block face

Explanation

Standing the tube on end puts the lumen perpendicular to the block face, so the microtome knife cuts across the wall and produces a complete ring. Embedding it lengthwise yields a longitudinal section instead.

Question 35Processing, Embedding, and Microtomy

Why is vacuum applied during tissue processing?

  1. To sterilize the tissue while it is being processed
  2. To speed reagent exchange and remove air Correct answer.
  3. To cool the tissue so it does not shrink
  4. To stop the alcohol from evaporating in the retort

Explanation

Vacuum pulls trapped air out of the tissue spaces so reagent enters faster and more completely, shortening processing schedules and improving infiltration of dense or fatty tissue. Heat and agitation often accompany vacuum for the same reason.

Question 36Processing, Embedding, and Microtomy

What is the result of holding paraffin far above its melting point for long periods?

  1. It becomes more fluid and infiltrates faster with no effect on tissue
  2. It causes the tissue to swell and crack at the edges
  3. It dissolves tissue lipids more completely, aiding sectioning
  4. The block becomes brittle and sections poorly Correct answer.

Explanation

Prolonged overheating drives off volatile components and oxidizes the wax, so blocks become hard and brittle and produce cracked or shattered sections. Wax should be kept just above its melting point and replaced on a schedule.

Question 37Processing, Embedding, and Microtomy

Why is agitation or stirring included in a tissue processing schedule?

  1. It reduces static electricity that builds up in the cassette
  2. It increases the rate of fluid exchange within the tissue Correct answer.
  3. It keeps the tissue cool during the hot paraffin steps
  4. It prevents the formation of formalin pigment in the tissue

Explanation

Moving reagent past the specimen reduces the unstirred layer at the tissue surface, so fresh reagent reaches the tissue and the schedule can be shortened. Agitation is a standard feature of automated processors for this reason.

Question 38Processing, Embedding, and Microtomy

What is the purpose of placing a biopsy pad or lens paper over small tissue fragments in a cassette?

  1. It holds small fragments securely and prevents loss Correct answer.
  2. It allows reagents to drain faster when processing ends
  3. It absorbs excess fixative so the tissue does not overfix
  4. It keeps the cassette lid from opening during processing

Explanation

Very small pieces can pass through cassette pores or be poured off with waste reagent, so a porous pad or lens paper keeps them contained. The material must be porous enough to allow free reagent exchange.

Question 39Processing, Embedding, and Microtomy

Tissue is carried from absolute alcohol into xylene, and the xylene turns cloudy. What does this indicate?

  1. The xylene has reached the end of its clearing capacity for wax
  2. The xylene is being used at too high a temperature
  3. The xylene has degraded into a colored byproduct
  4. The xylene has become contaminated with water Correct answer.

Explanation

Cloudiness means water has entered the clearing agent, usually because the absolute alcohol step was exhausted or the tissue was not fully dehydrated. Turbid xylene cannot clear tissue properly and should be replaced along with the alcohol.

Question 40Processing, Embedding, and Microtomy

A clearing agent must be miscible with which two substances?

  1. Paraffin and glycerol
  2. Water and xylene substitutes
  3. Formalin and water
  4. Alcohol and paraffin wax Correct answer.

Explanation

Clearing occupies the step between dehydration and infiltration, so the reagent must mix freely with the dehydrating alcohol it replaces and with the paraffin that replaces it. A reagent that is not miscible with either one leaves the tissue improperly cleared.

Question 41Processing, Embedding, and Microtomy

Which statement describes a limonene-based xylene substitute used in processing?

  1. It is non-flammable and replaces paraffin wax
  2. It is water-miscible and requires no dehydration step
  3. It is miscible with alcohol and paraffin and less toxic Correct answer.
  4. It must be heated to 60 °C to clear tissue adequately

Explanation

Terpene-based substitutes clear tissue by the same mechanism as xylene, being miscible with both alcohol and paraffin, while producing less irritating vapor. They are still flammable and require the same graded dehydration before use.

Question 42Processing, Embedding, and Microtomy

How should a skin biopsy be oriented in the block for evaluation of epidermal and dermal layers?

  1. On edge with the epidermis vertical Correct answer.
  2. At a 45-degree angle to the block face
  3. Lying flat with the epidermis face up
  4. Epidermis face down on the mold bottom

Explanation

Standing the specimen on edge places the epidermis and dermis at right angles to the knife, giving a full-thickness profile of all layers in one section. Lying flat produces sections that graze the epidermis tangentially.

Question 43Processing, Embedding, and Microtomy

When several tissue pieces are embedded in a single block, how should they be positioned?

  1. Placed at different depths to avoid collisions
  2. Stacked in layers to save mold space
  3. Separated by a thin layer of agar
  4. At the same level and not overlapping Correct answer.

Explanation

Pieces placed at the same plane and kept from overlapping are all reached by the knife at the same section level, so a single section shows every piece. Stacking causes some pieces to be cut before others or to be pushed out of the block.

Question 44Processing, Embedding, and Microtomy

Chatter, seen as alternating thick and thin section bands, most often results from which cause?

  1. Vibration from a loose block Correct answer.
  2. A flotation bath that is too cool
  3. Excessive trimming of the block face
  4. Use of charged or adhesive slides

Explanation

Chatter arises when the block or knife vibrates during the cutting stroke, commonly from a poorly clamped block, a loose blade, or very hard tissue. Tightening the block and blade and softening hard tissue reduce the artifact.

Question 45Processing, Embedding, and Microtomy

Section compression, in which the section is noticeably shorter than the block face, is best limited by doing what?

  1. Increasing the temperature of the water bath
  2. Setting the microtome for thicker sections
  3. Reducing the clearance angle to zero degrees
  4. Chilling the block and using a sharp blade Correct answer.

Explanation

Compression occurs when soft wax and a dull edge deform the section as it is cut, so cooling the block and using a sharp, correctly angled blade keep the section at its true dimensions. A very cold block or a large clearance angle will instead cause chatter.

Question 46Processing, Embedding, and Microtomy

What is the role of OCT compound in frozen sectioning?

  1. It supports the tissue during cutting Correct answer.
  2. It decalcifies the tissue before it is frozen
  3. It chemically fixes the tissue as it freezes
  4. It clears the tissue so it can be cut thin

Explanation

OCT is a water-soluble embedding medium that freezes with the tissue and holds it firmly to the chuck so thin sections can be cut. Because it is water-soluble, it is removed during routine staining without interfering with the tissue.

Question 47Processing, Embedding, and Microtomy

Which decalcifying agent is preferred when nucleic acid integrity and enzyme activity must be preserved?

  1. Formic acid
  2. Hydrochloric acid
  3. EDTA Correct answer.
  4. Nitric acid

Explanation

EDTA removes calcium by chelation at a near-neutral pH and is gentle on nucleic acids, enzymes, and antigens, although it acts slowly. Strong mineral acids decalcify rapidly but degrade these targets.

Question 48Processing, Embedding, and Microtomy

Overexposure of bone to a strong mineral acid decalcifying solution chiefly produces which effect?

  1. Marked swelling of the tissue
  2. Increased eosinophilia of collagen fibers
  3. Impaired nuclear staining and basophilia Correct answer.
  4. Loss of tissue lipids from the cytoplasm

Explanation

Acid hydrolysis removes nucleic acids, so nuclei lose their affinity for hematoxylin and appear pale or unstained. This is why acid decalcifiers must be stopped as soon as the endpoint is reached.

Question 49Processing, Embedding, and Microtomy

A block cuts with a smeared, wet appearance and the sections will not flatten on the bath. What is the most likely cause?

  1. Excessive paraffin infiltration of the tissue
  2. Incomplete dehydration or clearing Correct answer.
  3. A flotation bath set far too warm
  4. Over-dehydration of the tissue before clearing

Explanation

Residual water or clearing agent leaves the block soft and greasy, so sections smear, stick, and resist flattening. The remedy is to reprocess the tissue through fresh graded alcohols, clearing agent, and paraffin.

Question 50Processing, Embedding, and Microtomy

The clearance angle of a microtome knife is the angle between which two references?

  1. The cutting edge and the direction of travel
  2. The upper facet and the vertical clearance plane
  3. The lower bevel facet and the block face Correct answer.
  4. The two bevel facets of the cutting edge

Explanation

Clearance angle is measured between the lower ground facet of the blade and the plane of the block face; it must be just large enough to keep the facet from rubbing. The angle between the two facets is the bevel angle, a different measurement.