ASCP H flashcards

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

10% Neutral Buffered Formalin

NBF contains 4% formaldehyde w/v (10% formalin) buffered to pH 7.2–7.4 with phosphate salts; it is the standard fixative for routine histology, cross-linking proteins and preserving morphology for H&E and most IHC.

Fixative Penetration Rate

Formalin penetrates tissue at roughly 1 mm per hour from the surface, so thick specimens are sliced to about 3–4 mm thickness to allow complete fixation within a reasonable processing schedule.

Bouin Solution

A coagulant, non-additive fixative containing picric acid, formalin, and acetic acid; it preserves connective tissue well but must be washed out, and picric acid is explosive when dry.

Dehydration and Clearing

Dehydration removes water with graded ethanol; clearing then replaces ethanol with a solvent such as xylene that is miscible with both ethanol and paraffin, allowing molten paraffin to infiltrate and support the tissue.

Formalin Pigment

Brown granular acid hematin artifact deposited in blood-rich tissue when acidic formalin reacts with hemoglobin; it is removed from sections with saturated alcoholic picric acid before staining.

Routine Section Thickness

Paraffin sections for routine H&E are cut at 3–5 µm, while small biopsies and immunohistochemistry sections may be cut at 2–3 µm; thicker sections retain more dye and appear hyperchromatic.

Chatter Artifact

Fine parallel lines across a section caused by vibration during cutting, typically from a hard block, excessive cutting speed, a loose blade, or an improper clearance angle.

Cryostat Chamber Temperature

Frozen sections are usually cut with the chamber near −20 °C; warmer tissue causes smearing and folds, while colder tissue causes shattering and longitudinal cracking of the section.

Clearance Angle

The angle between the blade's cutting facet and the block face, usually 3–5 degrees; too small an angle causes compression and friction, too large an angle causes chatter and vibration.

Hematoxylin Staining Mechanism

Hematoxylin is a basic cationic dye complexed with an aluminum mordant that binds acidic nucleic acids, staining nuclei blue-purple; tissue elements staining this way are described as basophilic.

Bluing Step

After hematoxylin and differentiation, bluing in running tap water or Scott's tap water at about pH 8 converts the soluble red aluminum-hematin complex into an insoluble blue form.

Progressive versus Regressive Staining

In progressive staining dye is applied until the desired intensity is reached; in regressive staining the tissue is deliberately overstained and excess dye is then removed with acid alcohol, a step called differentiation.

Eosin Y

An acidic anionic dye applied at slightly acidic pH that stains cytoplasm, collagen, and red blood cells pink to red; structures that stain with eosin are termed eosinophilic.

PAS Reaction

Periodic acid oxidizes 1,2-glycol groups to aldehydes that react with Schiff reagent, producing magenta staining of glycogen, mucins, and basement membranes; diastase digestion distinguishes glycogen from other PAS-positive material.

Masson Trichrome Stain

A connective tissue stain in which collagen is colored blue by aniline blue or green by light green, while muscle and cytoplasm stain red with Biebrich scarlet–acid fuchsin and nuclei stain black.

Prussian Blue Stain

Hydrochloric acid releases iron from hemosiderin, which then reacts with potassium ferrocyanide to form an insoluble blue pigment; it demonstrates hemosiderin rather than other tissue iron forms.

Congo Red Stain

A stain that binds beta-pleated sheet proteins such as amyloid, appearing pink-red in ordinary light and showing apple-green birefringence under polarized light; the birefringence is the specific finding.

Alcian Blue pH 2.5

At pH 2.5 alcian blue stains both carboxylated and sulfated acid mucins blue; at pH 1.0 only the more strongly acidic sulfated mucins retain the dye.

Heat-Induced Epitope Retrieval

HIER heats sections to 95–100 °C in buffer, typically citrate pH 6.0 or Tris-EDTA pH 9.0, to break formalin cross-links and restore antigenicity that fixation masked.

Endogenous Peroxidase Block

Incubation in 3% hydrogen peroxide in water or methanol inactivates peroxidase naturally present in neutrophils, eosinophils, and red cells before a peroxidase-based detection system is applied.

DAB Chromogen

3,3'-Diaminobenzidine is oxidized by peroxidase to a brown, alcohol-insoluble precipitate, so stained slides can be dehydrated through alcohols and coverslipped with permanent resinous mounting media.

Endogenous Biotin

Liver and kidney contain native biotin that binds avidin-based detection systems and causes false-positive staining; it is blocked by sequential incubation with free avidin and then free biotin.

Negative Reagent Control

A section of the same tissue incubated with non-immune serum or an irrelevant antibody matched for isotype and concentration, confirming that observed staining is not nonspecific background.

Lot-to-Lot Reagent Verification

Before a new lot of stain or antibody enters service, it is run in parallel with the current in-use lot against known positive and negative control material and must give equivalent results.

Specimen Rejection Criteria

Specimens that are unlabeled, mislabeled, leaked, or received in the wrong fixative are not accessioned until the discrepancy has been documented and resolved with the submitting clinician or source.

FIFO Reagent Rotation

First-in, first-out stock rotation places newly received reagents behind older stock so that the oldest in-date material is consumed first, reducing waste and preventing use of expired reagents.

Levey-Jennings Chart

A control chart that plots daily control values against time with lines drawn at the mean and at plus or minus one, two, and three standard deviations, revealing systematic shifts and random scatter.

Westgard 1-3s Rule

A single control measurement falling beyond the mean plus or minus three standard deviations is a rejection rule that indicates random error and unacceptable run performance.

Root Cause Analysis

A structured investigation, often using the five whys or a fishbone diagram, that identifies the underlying process failure producing an error rather than blaming the individual involved.

Formaldehyde Exposure Limit

OSHA sets the permissible exposure limit for formaldehyde at 0.75 ppm as an 8-hour time-weighted average, with a 15-minute short-term exposure limit of 2 ppm.

Xylene Hazards

Xylene is a flammable aromatic hydrocarbon with a flash point near 27 °C; it is narcotic and irritates skin and eyes, and its OSHA permissible exposure limit is 100 ppm.

Chemical Hygiene Plan

A written plan required by the OSHA Laboratory Standard that describes standard operating procedures, engineering controls, personal protective equipment, and employee training for hazardous chemicals in the laboratory.