American Society for Clinical Pathology (ASCP) Histotechnologist Practice Test

What is the most specific technique for demonstrating amyloid in tissue samples?

1. Green birefringence following Congo red staining

2. Positive staining with Sudan black B

3. Demonstration of heparin in connective tissue

4. Thin layer chromatography for lipids

The correct answer is: Green birefringence following Congo red staining

The most specific technique for demonstrating amyloid in tissue samples is the green birefringence observed following Congo red staining. This technique involves using Congo red dye, which specifically binds to amyloid fibrils. When the stained tissue is viewed under polarized light, the amyloid appears bright green due to this birefringence. This characteristic is a hallmark of amyloid deposits, making this method not only sensitive but also specific for identifying amyloid. The other methods listed are relevant to different substances or conditions. For instance, positive staining with Sudan black B is primarily used to stain lipids, not amyloid. The demonstration of heparin in connective tissue is unrelated, as it pertains to different components of the extracellular matrix rather than amyloid. Lastly, thin layer chromatography is a technique commonly applied to separate and analyze lipids, and certainly does not serve the purpose of detecting amyloid. Therefore, the unique chemical interaction between Congo red and amyloid deposits, resulting in a distinct visual change under polarized light, underscores its specificity in identifying amyloid in tissue samples.