Why have chemical copper reduction methods largely fallen out of use in glucose measurement?

• A. They are expensive to run
• B. They require radioactive reagents
• C. Other reducing sugars can cause false increases of 5-15 mg/dL
• D. They are too slow

Answer: (C)

Copper reduction methods measure reducing capacity, not glucose alone. They rely on cupric ions being reduced by any reducing substance in the sample, so not only glucose but other reducing sugars or agents can produce the same color change or precipitate. This non-specificity means samples containing galactose, fructose, lactose, or other reducing substances can yield higher apparent glucose levels, typically by about 5–15 mg/dL. Because of this potential for false positives, these methods are less reliable for accurately quantifying glucose, and modern practice uses enzymatic assays that specifically detect glucose, reducing interference from other reducing substances.