AMCA MHTC key terms

The process of preserving tissue structure and preventing decay by chemically cross-linking or precipitating proteins so the sample remains stable for processing and staining.

An aqueous solution of formaldehyde gas, typically used at about 10 percent concentration, that cross-links proteins and is the most common routine tissue fixative.

Formalin adjusted with phosphate or other buffers to a near-neutral pH, reducing pigment artifact and preserving antigen and morphologic detail better than unbuffered solutions.

The interval between loss of blood supply to a tissue and the start of fixation, during which enzymatic degradation and morphologic change can begin.

The speed at which a fixative diffuses into tissue, roughly one millimeter per hour for formalin, meaning thick specimens fix unevenly unless sliced thin.

The standard working fixative made by diluting concentrated formalin with buffer to about four percent formaldehyde, used for routine immersion fixation of most surgical specimens.

A brown-black granular deposit formed when acidic formalin reacts with hemoglobin, often seen in bloody or poorly buffered tissue and removable with picric acid or alcohol washes.

Removal of calcium salts from bone or calcified tissue using acid or chelating agents so the specimen can be sectioned without tearing or shattering.

A chelating agent that removes calcium slowly and gently, preserving cellular detail and antigenicity better than strong acids during decalcification of bone specimens.

Stepwise removal of water from fixed tissue by immersion in increasing concentrations of alcohol, preparing it for clearing and infiltration with paraffin.

Replacement of dehydrating alcohol with a solvent such as xylene that is miscible with both alcohol and paraffin, making tissue translucent and ready for infiltration.

Saturation of cleared tissue with molten paraffin or other embedding medium so it hardens into a solid block that supports the specimen during sectioning.

Orienting and encasing an infiltrated specimen in a mold of paraffin or other medium so the desired cut surface faces the block face for sectioning.

Positioning the specimen in the embedding mold so that the diagnostically important surface, such as a mucosal edge or margin, lies parallel to the planned section plane.

A timed sequence of dehydration, clearing, and infiltration steps chosen for tissue type and size, balancing complete processing against over-hardening or shrinkage.

A precision instrument that advances a specimen or blade by set increments to cut uniformly thin sections from a paraffin block or frozen tissue.

The micrometer setting that determines how far the block advances per cut, commonly two to five micrometers for routine paraffin sections.

A continuous strip of serial sections that forms as the microtome cuts a well-processed paraffin block, later separated and floated onto slides.

A warm water bath used to flatten and stretch paraffin sections so they adhere smoothly to a glass slide without wrinkles or folds.

The attachment of a tissue section to a slide, aided by charged or coated slides, heat, or adhesives, preventing the section from detaching during staining.

A rapid method in which fresh or briefly fixed tissue is frozen and cut in a cryostat, providing intraoperative diagnoses within minutes without routine processing.

A refrigerated microtome chamber kept below freezing that allows cutting of frozen tissue sections for rapid diagnosis or for delicate antigen and lipid studies.

The exposed cut surface of the paraffin block that is presented to the blade, which must contain the full cross-section of the desired tissue.

The routine stain pairing a basic dye that colors nuclei blue-purple with an acidic counterstain that colors cytoplasm and connective tissue pink.

A staining approach in which the dye is applied until the desired intensity is reached, then stopped, rather than being overstained and selectively removed.

Controlled removal of excess dye from a stained section using acid alcohol or another agent to sharpen contrast between stained and unstained structures.

Adjusting hematoxylin-stained sections to a blue-purple color in a mildly alkaline solution after acid differentiation, stabilizing the nuclear stain.

A stain chosen to highlight specific substances such as collagen, mucin, iron, or microorganisms that routine hematoxylin and eosin does not demonstrate clearly.

A slide carrying known positive tissue run alongside test slides to confirm that a stain or reagent performed correctly and expected results were achieved.

Planned checks of reagents, equipment, and staining runs against defined acceptance criteria to detect problems before they affect reported patient results.

The documented corrective steps taken when quality control fails, such as repeating a run, replacing a reagent, or troubleshooting equipment before releasing results.

Systematic investigation of a problem such as poor staining or sectioning defects, working from observed signs back to likely causes and corrective steps.

Any structural change or deposit in a tissue section caused by handling, fixation, processing, or staining rather than by disease, which can mimic or obscure pathology.

An infection-control approach in which all blood and body fluids are treated as potentially infectious, requiring gloves, gowns, eye protection, and safe handling practices.

Barrier items such as gloves, lab coats, face shields, and respirators worn to protect the worker from chemical splashes, aerosols, and infectious material.

Placing blades, needles, and broken glass into rigid, puncture-resistant containers labeled for biohazard waste to prevent injury and exposure.

A ventilated enclosure that draws vapors away from the worker, used when handling formalin, xylene, and other volatile or hazardous laboratory chemicals.

A standardized document listing a chemical's hazards, handling precautions, exposure limits, and first-aid measures, kept accessible to laboratory staff.

An aromatic solvent used for clearing tissue and for deparaffinizing slides, flammable and hazardous to inhale, requiring ventilation and careful waste handling.

A glass slide coated with a positively charged layer that electrostatically binds tissue sections, reducing detachment during heat, enzyme, or harsh staining steps.

The date after which a reagent may no longer perform reliably, requiring replacement and documentation so that outdated solutions are not used in testing.

A manufacturer's identifier for a batch of reagent, recorded so that results can be traced and problems linked to a specific production lot if needed.