Congo Red

Question 1

What is the primary purpose of the Congo Red Method?

Answer 1

The demonstration of amyloid in tissues.

Question 2

Why is the Congo red method considered significant for demonstrating amyloid?

Answer 2

Because the resulting green birefringence is considered the most specific technique for identifying amyloid.

Question 3

What is the purpose of the alkali pretreatment in this method?

Answer 3

The alkali aids in the release of native internal hydrogen bonds between adjacent protein chains, making more potential sites available for dye binding.

Question 4

How is the dye believed to bind to amyloid at a molecular level?

Answer 4

Amyloid’s linear molecular configuration allows the azo and amine groups of the Congo red dye to form hydrogen bonds with similarly spaced hydroxyl radicals on the amyloid molecule.

Question 5

What are the preferred fixatives for this method?

Answer 5

Alcohol or Carnoy solution is preferred.

Question 6

What is the effect of prolonged storage in 10% formalin on tissue to be stained with this method?

Answer 6

Prolonged storage in 10% formalin will cause a gradual decrease in staining intensity.

Question 7

At what thickness should paraffin sections be cut for this technique, and why?

Answer 7

Sections should be cut at 8 to 10 μm because sections not in this range may not show the green birefringence.

Question 8

what is a key recommendation for control sections?

Answer 8

It is better not to keep too many control sections cut in advance, because the staining intensity has been reported to decrease with the age of the sections.

Question 9

How does the age and size of amyloid deposits affect the intensity of histochemical reactions?

Answer 9

Massive, presumably long-standing deposits give less intense histochemical reactions than small, newly formed deposits.

Question 10

What is the corrective action for a slide with “No nuclear stain”?

Answer 10

Submit the slide as is, or recut and restain the sample.

Question 11

What is the likely cause and corrective action if the Hematoxylin is “not acidified”?

Answer 11

The cause is a technical error in the staining process. The corrective action is to recut and restain the sample. (The tissue will have a lot of background staining)

Question 12

A slide shows “Pale target tissue components.” What are two possible, correctable reasons for this?

Answer 12

Inadequate time in Solution B.
The working solution was not prepared immediately before use.

Question 13

A slide shows “Pale target tissue components” due to “Prolonged fixation.” What is the recommended corrective action?

Answer 13

This problem cannot be corrected.