PAS

Question 1

What is the purpose of the PAS reaction?

Answer 1

To demonstrate polysaccharides, neutral mucosubstances, and basement membranes.

Question 2

What is the fundamental principle of the PAS reaction?

Answer 2

It is based on the oxidation of certain tissue elements (like 1,2 glycol groups) to aldehydes by periodic acid, which are then detected by the Schiff reagent.

Question 3

What is the name of the colorless compound formed when basic fuchsin is treated with sulfurous acid to create the Schiff reagent?

Answer 3

Leucofuchsin.

Question 4

What happens during the washing step in running water after the tissue has been treated with Schiff reagent?

Answer 4

The running water causes the loss of the bound sulfurous acid group, which restores the quinoid structure in the dye, resulting in the visualization of the typical magenta color.

Question 5

What are two recommended fixatives for the PAS reaction?

Answer 5

10% neutral-buffered formalin or Bouin’s solution.

Question 6

At what thickness should routine paraffin sections be cut for the PAS stain?

Answer 6

4 to 5 μm.

Question 7

If specifically staining kidney sections, what thickness is recommended?

Answer 7

1 to 2 μm.

Question 8

What is the most sensitive tissue for use as a quality control in the PAS reaction?

Answer 8

A section of kidney

Question 9

If the PAS procedure is being used to demonstrate glycogen (including a diastase digestion control), what tissues are recommended for quality control?

Answer 9

A section of liver containing glycogen or a section of cervix (including both endocervix and ectocervix).

Question 10

List at least five tissue elements or structures that will show a positive PAS reaction.

Answer 10

Glycogen

Neutral mucosubstances

Basement membranes

Fungal walls

Thyroid colloid

Certain epithelial sulfated mucins and sialomucins

Colloid material of the pars intermedia of the pituitary

Question 11

What is the corrective action if the wrong fixative was used?

Answer 11

Recut and restain.

Question 12

What is the corrective action for delayed fixation?

Answer 12

Recut and restain.

Question 13

What is the corrective action for an inadequate or omitted oxidation step?

Answer 13

Recut and restain.

Question 14

What is the corrective action if the section was over-oxidized (left in periodic acid too long)?

Answer 14

Recut and restain.

Question 15

What is the corrective action if the Schiff reagent used was old?

Answer 15

Recut and restain.

Question 16

What is the corrective action if the primary stain was omitted or applied for a very short time?

Answer 16

Recut and restain.

Question 17

What is the corrective action if diastase digestion occurred (when it shouldn’t have)?

Answer 17

Recut and restain.

Question 18

What is the corrective action if the Schiff reagent dried out on the slide?

Answer 18

Recut and restain.

Question 19

What should you do if the nuclear stain (hematoxylin) was not applied?

Answer 19

Go back to water and reapply hematoxylin.

Question 20

What is the corrective action if the section was over-differentiated in acid alcohol?

Answer 20

Go back to water and reapply hematoxylin. Ensure timing of each step is correct and that fresh solutions are used.

Question 21

What is the corrective action if the hematoxylin was over-oxidized?

Answer 21

Go back to water and reapply hematoxylin. Ensure timing of each step is correct and that fresh solutions are used.