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Re: More about the urine in alkaptonuria

Dear Editor

I would like to mention a few interesting points about the urine in alkaptonuria.[1] When testing for the presence urine sugar by Benedict's method, an alkaptonuric specimen gives a strongly positive (falsely, of course) reaction, producing an orange precipitate. However, the clue lies in the supernatant which turns black. Glucose oxidase-based test does not give a positive reaction in this setting. Such a discrepancy if encountered, one should be astute enough to strongly consider alkaptonuria.

Interestingly, alkaptonuric mice neither pass black urine nor do they develop pigmentation. Thanks to their ability to synthesise vitamin-C on their own, which we humans have lost during evolution.

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