Thormaehlen Reaction

THORMAEHLEN REACTION (Thormaehlen) was first discovered by Thormaehlen in 1887 and is used to determine melanogen in urine; it is pathognomonic for the presence of melanoma tumors in the body. The principle of the reaction is similar to Legault's test for acetone (see Legault's test), but upon the addition of glacial acetic acid an immediate blue coloration is obtained. This coloration in the Thormaehlen reaction is due to the presence in the urine of intermediate products in the formation of melanin-derivatives of pyrrole and indole. In performing the reaction, it is necessary to bear in mind that an excessive amount of reagents can lead to an erroneous conclusion due to the possibility of side reactions. The exact dosage is given by Yuivu-Mu, according to whom 5 drops of freshly prepared 3% nitroprusside of sodium and 2 drops of 10% caustic soda are added to 2 cm³ of urine; the purple or red-brown color of the solution resulting from the addition of alkali turns into a persistent blue color upon the addition of 4-5 drops of glacial acetic acid. The reaction is very sensitive and makes it possible to detect the presence of indole in a dilution of 1:40,000. According to some authors, the reaction can be positive in the urine of healthy people upon exposure to sunlight.