Glucose Sugar in the Urine (e.g. Glucosuria) - Reducing Sugars vs. Non-reducing Sugars -Biochemistry

Carbohydrates are classified by the number of carbon atoms as trioses, tetroses, pentoses, and hexoses, and by their functional groups as aldoses (aldehyde group) or ketoses (ketone group). Examples include glyceraldehyde (triose), ribose (pentose), and glucose, fructose, and galactose (hexoses).

Oxidation involves gaining oxygen, losing hydrogen, or losing electrons, while reduction is the opposite. A reducing agent is a substance that reduces another substance while being oxidized itself.

Reducing sugars are capable of being oxidized and therefore reduce other substances. All aldose sugars are reducing sugars because their open-chain form exposes the carbonyl group for reaction. Ketoses, like fructose, can also act as reducing sugars through a process called tautomerization (keto-enol shift).

The presence of reducing sugars can be detected using the Tollens reagent (silver mirror test) or the Benedict/Fehling reagent (red precipitate). A positive result indicates the presence of a reducing sugar such as glucose, galactose, or fructose.

To specifically test for glucose, the glucose oxidase enzyme can be used. If the enzyme reacts, the sample contains glucose. The presence of glucose in urine (glucosuria) is discussed, noting it can be normal during pregnancy or indicate gestational diabetes.