Significance of Staining Uric Acid Crystals with Natural and Synthetic Dyes

Abstract

In the urinary sediment of healthy and of sick people only crystals of uric acid appear stained (yellow-brown). No other colored metabolites or calciumsalts in crystallized form are excreted. There is no uniform opinion about the nature of this yellow-brown pigment (1;2;3;); it is probably a mixture of urobilin — urobilinogen. Among the many pigments appearing in the urine of healthy individuals, two are chemically and biochemically well-known: urobilin and urorosein. Experiments with urobilin would have required the production of this bilirubin derivative in sufficient quantities; this task was beyond our technical conditions at that time. Studies to try staining with urorosein, on the other hand, were easy because its synthesis from its basic substance, indole-acetic-acid (4;5;) is easy (6;7;8;). It seemed, furthermore, obvious to experiment with another natural pigment of strong staining property, beetroot extract. Since both kinds of dye studies proved successful it was but a simple, logical step to test a synthetic dye also: methylene blue.