Diabetes mellitus is a disease where the body cannot control blood glucose concentration within normal limits.

It can occur due to lack of insulin production or failure of cells to respond to insulin.

The presence of glucose in urine can indicate diabetes because it shows that not all of the glucose in filtrate has been reabsorbed into the blood in the kidneys. This indicates that the blood glucose level exceeds a healthy threshold.

The enzymes on test strips that can test for glucose are glucose oxidase and peroxidase.

The enzymes are immobilised on a pad at the end of the test strip and catalyse reactions that change the colour of the pad when they are immersed in urine that contains glucose.

Glucose oxidase catalyses the reaction between glucose and oxygen, forming gluconic acid and hydrogen peroxide.

Peroxidase catalyses a reaction between hydrogen peroxide and a colourless chemical to form a coloured compound and water.

This colour change indicates the presence of glucose in urine.

The resulting colour of the pad is matched against a colour chart. The darker the colour, the higher the glucose concentration.

The glucose test gives negative results for other sugars because glucose oxidase is specific for glucose, so it does not react with other sugars to produce the colour change.

Urine tests do not indicate the current blood glucose concentration. They only show if the concentration was previously too high.

A biosensor allows people with diabetes to check their blood glucose concentration using a small sample of blood.

Any glucose in the blood passes into the device and its oxidation is catalysed by glucose oxidase. The hydrogen peroxide produced is then oxidised, the electron flow from which is proportional to glucose concentration.