Fixation

Question 1

Non-coagulant fixatives

Answer 1

Formaldehyde
Gluteraldehyde
Glyoxal
Osmium tetroxide
Potassium dichromate

Question 2

Nonadditive fixatives

Answer 2

Alcohols
Acetone
Acetic acid

Question 3

Coagulant fixatives

Answer 3

Alcohol/acetone/acetic acid
Mercuric chloride
Chromic acid
Picric acid
Zinc salts
Cupric salts

Question 4

Davidson

Answer 4

NBF, ethanol, acetic acid

Good for eyes and testis
Store in 70% alcohol after fix

Question 5

Orth Solution

Answer 5

Potassium dichromate, sodium sulfate +formaldehyde

Good for chromaffin granules (cytoplasm of cells in adrenal madulla)
Wash after fixation, controlled time, store in 70-80% alcohol

Question 6

B5

Answer 6

Mercuric chloride, sodium acetate, formaldehyde

Good for nuclear detail
Treat with iodine then sodium thiosulfate
Store in 70% alcohol

Question 7

Zenker & Helly

Answer 7

Mercuric chloride, potassium dichromate +formaldehyde

Wash with water
Fix for 24 hrs then 70-80% alcohol

Question 8

Bouin

Answer 8

Picric acid, formaldehyde, acetic acid

Lyses RBCs, preserves connective tissue, GI biopsies
Good for trichrome and H&E
Wash yellow color with 50-70% alcohol

Question 9

Gendre (alcoholic Bouin)

Answer 9

95% Alcohol, picric acid, formaldehyde, acetic acid

Preserves some carbohydrates (glycogen)

Question 10

Hollande solution

Answer 10

Copper acetate, picric acid, formaldehyde, acetic acid

Decalcifies small bone specimens
Good for GI biopsies
Wash before processing

Question 11

Zamboni (PAF)

Answer 11

Paraformaldehyde, picric acid, sodium phosphate dibasic/monobasic

Good for EM and general purpose
Final pH 7.5
Allows secondary fixation with osmium tetroxide

Question 12

Zinc formalin solutions

Answer 12

Antigenicity remains long term use (zinc prevents crosslinking)
Fixes more rapidly that formalin alone

Question 13

Acetone fixation

Answer 13

Non-additive coagulant
Used for demonstration enzymes (acid and alkaline phosphatase)
For brain specimens for rabies
Overhardens and over shrinks

Question 14

Carnoy solution

Answer 14

Absolute alcohol, chloroform, acetic acid

Lyses RBCs
Preserves glycogen
Fast acting
Shrinkage and hardening

Question 15

Fixatives for electron microscopy

Answer 15

Osmium tetroxide, aldehydes, and buffered PAF (Zamboni)

Question 16

Osmium tetroxide advantages

Answer 16

Good preservation of cytologic detail
Renders lipids insoluble (good membrane preservation)

Question 17

Osmium tetroxide disadvantages

Answer 17

Can only be used for 2-4hrs
Penetrates poorly (must be cut into 1mm cubes)
No IHC

Question 18

Aldehyde fixation advantages (5)

Answer 18

Better penetration of fixative
IHC can be done
Specimen can be in fixative for a long time
Used for light and EM
Used easily for perfusion of tissues

Question 19

Aldehyde fixation disadvantages (3)

Answer 19

Lipids not preserved (unless secondary fixation with osmium tetroxide)

Membrane-bound cavities enlarged

Membranes electron lucent (unless secondary fixation used)

Question 20

Buffered PAF (Zamboni) advantages

Answer 20

Can be in fixative RT indefinitely
Penetrates rapidly and stabilizes
Both light and EM

Question 21

Buffered PAF (Zamboni) disadvantages (3)

Answer 21

Lipids not preserved (unless secondary fixation with osmium tetroxide)

Cytoplasmic granules and lysosomes not preserved

Background substance not preserved