Objective: Amyloidosis represents a group of diseases with deposition of amyloid fibrils. Clinical and histopathological features of renal amyloidosis vary according to the type of precursor protein. Histopathological diagnosis of amyloidosis relies on routine Congo red histochemistry. Thioflavin T may be an alternative method based on examination on ultraviolet light, but is believed to give inconsistent and inaccurate results.

Materials and Method: The sensitivity and specivity of Thioflavin T and Congo red fluorescence that can be applied to the diagnosis of amyloid were compared in order to find how best to diagnose amyloid deposits on fluorescence microscopy.

Results: Frozen tissue sections available from 120 native and transplant renal biopsy patients were stained with Tioflavin T. Prospectively, 10 cases of amyloidosis (8 with AA and 2 with nonAA) were diagnosed on frozen Tioflavin T sections and identical Congo red fluorescence staining was found in all the cases. There were no false positives or negatives.

Conclusion: The Tioflavin T method is simple to perform and easier to evaluate. It can therefore be utilized to track down even minute amyloid deposits, which might be missed by the Congo red fluorescence. In conclusion, Tioflavin T was demonstrated to be a sensitive and specific method for diagnosis of amyloid even in small frozen renal tissue sections. This method can, therefore, allow the easiest diagnosis of renal amyloidosis on fluorescence microscopy.