ASCP HT flashcards

32 cards. Read the term and the definition here. The deck at the top of this page is optional.

10% neutral buffered formalin

Most widely used fixative; contains 4% formaldehyde buffered to pH 7.0-7.4, cross-links proteins, and penetrates tissue at roughly 1 mm per hour.

Fixative-to-tissue volume ratio

Minimum ratio is 10 parts fixative to 1 part tissue; less fluid leads to incomplete fixation and formalin pigment as the solution becomes acidic.

Cold ischemia time

Interval from interruption of blood supply in the patient to immersion of the specimen in fixative; prolonged times degrade DNA, RNA, and phosphorylated epitopes.

EDTA decalcification

Neutral-pH chelating agent that removes calcium slowly; gentler than nitric or hydrochloric acid and preserves antigens and nucleic acids for IHC and molecular testing.

Formalin pigment

Brown acid hematin deposit that forms in acidic or unbuffered formalin, especially in blood-rich tissue; it is removed by saturated alcoholic picric acid.

Bouin solution

Picric acid-formalin-acetic acid coagulant fixative that preserves glycogen and connective tissue; tissues must be washed in alcohol to remove the yellow picric acid.

Xylene

Aromatic clearing agent miscible with both ethanol and molten paraffin; it removes dehydrant from tissue so paraffin can infiltrate, and it is flammable and neurotoxic.

Paraffin melting point

Routine paraffin melts at 56-60 degrees C for infiltration; the flotation bath is set 5-10 degrees C lower, at about 40-45 degrees C.

Routine section thickness

H&E sections are cut at 3-5 micrometres, small biopsies and kidney at 2-3 micrometres, and immunohistochemistry or FISH sections at 4-5 micrometres.

Clearance angle

Angle between the knife bevel and the block face, usually 3-8 degrees; too little produces chatter, too much causes uneven or skipped sections.

Cryostat temperature

Chamber is held near minus 20 to minus 25 degrees C for routine frozen sections, which are cut 4-6 micrometres and fixed in cold formalin or acetone.

Chatter artifact

Parallel thick-and-thin bands across the section caused by a loose block, dull blade, vibration, or hard tissue; corrected by tightening the block and changing the blade.

Ammonium oxalate test

Chemical endpoint test for decalcification: fluid mixed with ammonium oxalate forms a calcium oxalate precipitate while calcium remains, and no precipitate means completion.

Hematoxylin

Basic cationic dye oxidized to hematein and complexed with aluminum; the complex stains nucleic acids blue-purple and serves as the nuclear stain in H&E.

Eosin

Acidic anionic dye applied at slightly acidic pH after bluing; it stains cytoplasm, collagen, and red blood cells pink in the H&E sequence.

Bluing

Raising section pH with Scott's tap water or lithium carbonate after hematoxylin, converting red alum-hematin to the blue color seen in stained nuclei.

PAS reaction

Periodic acid oxidizes 1,2-glycol groups to aldehydes that react with Schiff reagent, staining glycogen, mucins, and basement membranes magenta; diastase controls glycogen.

Prussian blue

Iron stain in which hydrochloric acid releases ferric iron that reacts with potassium ferrocyanide; hemosiderin deposits appear blue against a red counterstain.

Congo red

Alkaline dye that binds amyloid deposits and shows apple-green birefringence under polarized light; a known positive control is required for interpretation.

GMS stain

Grocott methenamine silver stain: chromic acid oxidizes carbohydrates, silver reduces to black on fungal walls, and a green counterstain provides contrast.

Heat-induced epitope retrieval

Heating sections in citrate pH 6.0 or EDTA pH 8.0-9.0 by pressure cooker, steamer, or microwave to break formalin cross-links and unmask antigens before immunostaining.

DAB chromogen

Diaminobenzidine plus peroxidase gives an insoluble brown precipitate that resists alcohol, so stained slides can be dehydrated, cleared, and coverslipped routinely.

Isotype negative control

Irrelevant antibody matched to the primary in species and immunoglobulin class, applied to a serial section to reveal nonspecific background binding.

HER2 FISH positive

Per ASCO/CAP, a HER2 to CEP17 ratio of 2.0 or greater, or average HER2 copies of 6.0 or more per nucleus in the invasive tumor cell population.

ER positivity threshold

By ASCO/CAP, any nuclear estrogen receptor staining in 1% or more of invasive tumor cells is reported as positive; lower staining is reported as negative.

FFPE nucleic acid quality

Formalin cross-linking and fragmentation limit usable amplicon size; cold ischemia and fixation times must be controlled and documented for molecular assays.

Formaldehyde exposure limit

OSHA permissible exposure limit is 0.75 ppm as an 8-hour time-weighted average, with a 2 ppm short-term exposure limit not to be exceeded.

Formalin spill neutralization

Absorb the spill with pads, neutralize with ammonium hydroxide or sodium bisulfite, then collect as hazardous waste while wearing gloves, goggles, and respiratory protection as needed.

Safety data sheet

GHS document of 16 sections covering hazards, composition, first aid, handling, storage, exposure controls, and disposal; accessible for every hazardous laboratory chemical.

Temperature log

Daily documented record of processor, embedding center, flotation bath, refrigerator at 2-8 degrees C, and freezer temperatures, used as instrument quality control.

Proficiency testing

External CAP/CLIA-required evaluation of laboratory staining and interpretation, including predictive markers such as ER, PR, and HER2, with documented review and corrective action.

Slide label requirement

Each slide must carry two patient identifiers plus specimen source and date, and must be verified against the requisition before staining and interpretation.