Stokes' Congo Red
for Amyloid

Solutions

Mayer's hemalum

80% ethanol

Alkaline Congo Red
Congo red	as	required
Ethanol, 80%	100	mL
Potassium hydroxide	0.2	g

Dissolve the potassium hydroxide in the ethanol.

Add sufficient dye to saturate. Leave overnight and filter.

Stable for about 3 months.

Tissue sample
5µ paraffin sections of neutral buffered formalin fixed tissue are suitable.
Other fixatives are likely to be satisfactory.
Frozen sections are suitable.

Method

1. Bring sections to water via xylene and ethanol.
2. Place into alkaline congo red for 25 minutes.
3. Wash with tap water for 5 minutes.
4. Stain nuclei with Mayer's hemalum for 5 minutes.
5. Blue in running tap water for 10 minutes.
6. Dehydrate rapidly in absolute ethanol.
7. Clear with xylene and mount with a resinous medium.

Expected results

• Amyloid  –  orange to red
• Nuclei  –  blue
• Background  –  colourless

Notes

1. If congo red is applied for longer than 25 minutes, the background will show some colouration.
2. Green birefringence is displayed under crossed polarisers.

 

Reference
Stokes, Gwen, (1976),
An improved congo red method for amyloid,
Medical Laboratory Sciences, v 33, 79

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