Higher detectability of amyloid with phenol Congo red compared with alkaline Congo red

Area of Science:

• Pathology
• Histochemistry
• Medical Diagnostics

Background:

• Amyloidosis involves abnormal protein deposition, damaging organs and requiring early histological confirmation.
• Current gold standard, alkaline Congo red (ACR) staining, has limited sensitivity for detecting minimal amyloid deposits.
• A simpler, more sensitive screening method is needed for early amyloidosis diagnosis.

Purpose of the Study:

• To compare the diagnostic performance of phenol Congo red (PHCR) and alkaline Congo red (ACR) staining techniques for detecting minimal amyloid deposits.
• To evaluate PHCR as a potential screening tool for early amyloidosis detection.

Main Methods:

• 452 tissue specimens from 425 patients with suspected amyloidosis were analyzed.
• Adjacent tissue sections were stained using both ACR and PHCR methods.
• Immunohistochemistry was used for amyloid typing in positive cases; Cohen's κ coefficient assessed method agreement.

Main Results:

• 169 specimens (37%) tested positive for amyloid.
• PHCR staining detected more positive cases (75) than ACR alone (1).
• The methods showed 83% agreement (Cohen's κ = 0.60), indicating moderate consistency.

Conclusions:

• Phenol Congo red (PHCR) staining enhances the detection of amyloid (light chain, transthyretin, amyloid A protein) in various tissues.
• PHCR serves as an effective screening method for suspected amyloidosis, improving early diagnosis.
• Further verification of PHCR specificity using electron microscopy or mass spectrometry is recommended.