Screening for Amyloid with the Thioflavin-T Fluorescent Method

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Abstract
Recently a staining method for amyloid was described using the fluorochrome thioflavin-T. While several papers have appeared indicating its usefulness, the question of false positivity has been treated only briefly. By screening a number of consecutive surgical specimens, as well as several known amyloid controls, it was found that false positives do indeed occur. While these usually offer little diagnostic difficulty, substances other than amyloid fluoresce with this stain, and, therefore, the method should not be regarded as specific. Since dichroic birefringence with congo red is probably the most sensitive and specific histochemical test for amyloid, it is suggested that thioflavin-T be used as a rapid screening method, but that the presence of amyloid must be confirmed using the former technique, or other confirmatory tests such as crystal violet metachromasia or the electron microscopic morphology.