The patient’s urine contains glucose.

You explain to Monica that the orange-red precipitate indicates that the urine sample contains glucose. You can’t quite remember how the test works though. 

Monica explains that Fehling's test is based on the reduction of copper(II) ions (Cu²⁺) to copper(I) ions (Cu⁺) by reducing sugars under alkaline conditions. This gives the solution an orange-red precipitate. Monica goes on to add that the test seems to have worked fine since it did not yield a positive result for sucrose, a non-reducing sugar.

[Sucrose must be broken down into its constituent monosaccharide units before Fehling’s test can be carried out. If sucrose is boiled with diluted hydrochloric acid, it will be hydrolyzed to glucose and fructose. It will then give a positive Fehling’s test.]

However, Monica is not entirely sure that a positive Fehling’s test is a definite diagnostic test for diabetes. You explain to Monica that while glucose in the urine can indicate diabetes, there could also be other explanations for its presence, including medication and kidney disease. Therefore, further tests should be carried out for a definitive diagnosis. 

You and Monica are satisfied that you have carried out the test properly and can now present the results to Dr. Brown.