In ancient Greece the father of Medicine, Hypocrates, described a method of diagnosing diabetes mellitus by tasting the patient's urine. What is the physiological explanation for this archaic method?

Under normal conditions the glucose filtered by the renal glomeruli is almost completely resorbed in the nephron tubules and not excreted in urine. With the elevated glucose blood level the renal tubules cannot resorb all the filtered glucose and some amount of the substance appears in the urine. This amount is enough to give the sweet taste that helped Hypocrates to diagnose diabetes and to differentiate it from other diseases accompanied by polyuria. Nowadays the method is inconceivable because of the danger of contamination of the tester by disease agents possibly there in the patient's urine.

The Endocrine System - Image Diversity: Hypocrates