ASCP HT key terms

The process of preserving tissue by stabilizing proteins and other molecules so cells resist autolysis and putrefaction and keep their structure through processing and staining.

A fixative of formaldehyde dissolved in water at about 10% concentration and buffered to pH 7.0-7.4 with phosphate salts; the standard routine fixative for surgical tissue.

The interval from when a specimen loses its blood supply in the operating room to when it is placed in fixative; longer times degrade DNA, RNA, and proteins.

Self-digestion of cells by their own enzymes after death or loss of blood supply, which erodes nuclear detail and weakens staining if fixation is delayed.

Removal of calcium salts from bone and other calcified tissue with acid or chelating agents so the specimen can be sectioned without tearing or knife damage.

Applying colored dyes to the cut edges of an excision specimen so the pathologist can recognize the margin on the slide and judge whether the lesion was completely removed.

The processing step in which water is removed from tissue by passing it through graded alcohols, preparing it to accept a clearing agent.

Replacing alcohol in tissue with a fluid miscible with both alcohol and paraffin, such as xylene, which makes the specimen translucent and ready for infiltration.

Saturating cleared tissue with melted paraffin or another embedding medium, often under vacuum, so the interior is supported and can be cut into thin sections.

Positioning the infiltrated specimen in a mold and surrounding it with paraffin or another medium that hardens into a block suitable for microtomy.

Cutting thin, uniform sections from a paraffin block on a microtome; routine surgical sections are commonly cut at 3 to 5 micrometers.

Fine parallel lines, scratches, or alternating thick and thin areas in a section, usually caused by block or blade vibration, a loose knife, or overhard tissue.

Thinning, wrinkling, or crinkling of a section as it is cut, often resulting from a dull blade, an overly warm block, or cutting too quickly.

A microtome housed in a refrigerated cabinet that cuts unfixed, frozen tissue quickly, most often for intraoperative diagnosis or lipid and enzyme studies.

A basic dye that, complexed with a metal mordant such as aluminum, stains nuclei purple-blue by binding to chromatin and other acidic components.

An acidic, pink-orange dye that stains cytoplasm, collagen, and other basic proteins, providing contrast to the blue nuclei in the routine H&E stain.

A method in which dye is applied until the desired intensity is reached and no destaining step is needed, so timing and dye strength must be controlled.

A method in which tissue is deliberately overstained, then destained with acid alcohol or a similar agent until only the target structures keep color.

Treating hematoxylin-stained sections with a weak alkaline solution so the reddish-purple dye converts to a stable blue, typically done in tap water or a bluing reagent.

A phenomenon in which a dye colors certain tissue substances a different hue from the dye solution itself, such as cartilage appearing purple with toluidine blue.

A stain in which periodic acid oxidizes carbohydrates and Schiff reagent then colors them magenta, highlighting glycogen, mucin, fungi, and basement membranes.

A stain that demonstrates hemosiderin by releasing ferric iron from tissue stores and precipitating it as an insoluble blue pigment.

A dye that binds amyloid, appearing orange-red in brightfield and showing apple-green birefringence when the section is examined under polarized light.

A contrasting dye applied after the primary stain to color background structures so they can be distinguished from the target of interest.

The specific small site on an antigen where an antibody binds; fixation can hide or alter epitopes, which is why retrieval steps are often needed.

A treatment that re-exposes epitopes masked by formalin fixation, either by heating sections in buffer (HIER) or by enzymatic digestion (PIER).

An antibody produced by a single cloned cell line that recognizes one epitope, giving consistent staining but sometimes less sensitivity than a polyclonal reagent.

A detection method using a polymer backbone carrying many enzyme molecules and secondary antibodies, which amplifies signal while reducing background compared with avidin-biotin methods.

A soluble compound that an enzyme converts into an insoluble colored deposit at the site of antibody binding, such as DAB producing a brown product.

Peroxidase activity naturally present in tissue, especially red blood cells and granulocytes, that can react with chromogen and mimic a true positive unless blocked.

A technique in which labeled nucleic acid probes bind to complementary DNA or RNA sequences within intact tissue sections, allowing localization of specific genes or transcripts.

A method in which fluorescently labeled probes bind to chromosome targets in tissue or cell preparations, used to detect gene amplification, deletion, or translocation.

A tissue known to contain the antigen under test, processed alongside the patient slide to show that the antibody and detection system worked correctly.

Planned checks performed during testing, such as control slides and new reagent verification, that show a run met defined criteria before results are released.

A program that sends unknown specimens to a laboratory and compares its results with peer laboratories, revealing accuracy problems and systematic errors.

A standardized document describing a chemical's hazards, safe handling, storage, spill response, and first aid, kept accessible to everyone in the laboratory.

The legal maximum airborne concentration of a chemical to which a worker may be exposed over a work shift, set for substances such as formaldehyde and xylene.

A written laboratory program covering safe work practices, engineering controls, training, and emergency procedures for handling hazardous chemicals.

Scheduled cleaning, inspection, and servicing of instruments such as tissue processors, microtomes, and stainers to prevent breakdowns and staining failures.