A urinalysis on a 3-year-old reveals a positive copper reduction test and a negative glucose oxidase test. How would these results be interpreted?

A urinalysis on a 3-year-old reveals a positive copper reduction test and a negative glucose oxidase test. How would these results be interpreted?

• A. Glucose is present
• B. Galactose is present
• C. Lactose is present
• D. Mannose is present

Answer: (B)

Reducing substances in urine are detected by the copper reduction (Benedict’s) test, which turns positive when a sugar with a free aldehyde or ketone group can reduce Cu2+ to Cu+. The glucose oxidase test, on the other hand, is specific for glucose; a negative result means glucose isn’t present. So this pattern shows there is a reducing sugar in the urine, but not glucose. In a child, the classic non-glucose reducing sugar that would yield this pattern is galactose, as seen in galactosemia, where galactose appears in the urine and Benedict’s test is positive while the glucose oxidase test remains negative. Therefore, the interpretation is that galactose is present in the urine.

Reducing substances in urine are detected by the copper reduction (Benedict’s) test, which turns positive when a sugar with a free aldehyde or ketone group can reduce Cu2+ to Cu+. The glucose oxidase test, on the other hand, is specific for glucose; a negative result means glucose isn’t present. So this pattern shows there is a reducing sugar in the urine, but not glucose. In a child, the classic non-glucose reducing sugar that would yield this pattern is galactose, as seen in galactosemia, where galactose appears in the urine and Benedict’s test is positive while the glucose oxidase test remains negative. Therefore, the interpretation is that galactose is present in the urine.