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Alkaptonuria is a rare metabolic anomaly characterized by the tendency of the urine to turn dark on exposure to air, owing to the fact that the urine contains homogentisic acid. The constitution of this compound, which is chemically 1-4 dihydroxyphenylacetic acid shows that it may be regarded as a derivative of hydroquinone and points the way to its instant detection in urine.
The urine is made strongly alkaline with sodium or potassium hydroxide and dropped on regulation sensitized photographic paper. Wherever a drop of the urine touches the paper the latter turns coal black instantly, a process exactly similar to that used in everyday photography. This may be done in full daylight.
We have found no other substance present in urine, either normally or pathologically, which is capable of reducing the photographic paper in this manner. Diabetic urine, no matter how high the concentration of reducing sugar, remains without effect.
Fishberg EH. THE INSTANTANEOUS DIAGNOSIS OF ALKAPTONURIA ON A SINGLE DROP OF URINE. JAMA. 1942;119(11):882. doi:10.1001/jama.1942.72830280001009