Measuring the Concentration of Glucose in Urine

This lesson covers: 

1. What diabetes mellitus is
2. Using glucose test strips to screen for diabetes
3. Limitations of urine glucose tests
4. Biosensor technology for blood glucose monitoring

Using glucose test strips to identify diabetes

Diabetes mellitus is a medical condition where the body struggles to regulate blood glucose levels properly. This happens due to problems with the production or effectiveness of insulin, a hormone that helps cells absorb glucose from the blood.

Glucose in urine above a normal limit known as the renal threshold may indicate diabetes. This occurs when blood levels rise so high that the kidneys cannot reabsorb all filtered glucose.

Urine glucose test strips work as follows:

1. The strip pad contains immobilised glucose oxidase and peroxidase enzymes.
2. A test strip is dipped in a urine sample.
3. Glucose oxidase oxidises any glucose present into gluconic acid and hydrogen peroxide.
4. Peroxidase then uses the hydrogen peroxide to oxidise a colourless chromogen into a brown compound.
5. The colour change produced is proportional to the glucose concentration (the darker the colour, the higher the glucose level).
6. The colour is matched to a reference chart to determine the approximate glucose level in urine.

The strip method is specific to glucose due to the specificity of glucose oxidase, so it gives negative results for other sugars that might be in urine.

Limitations of urine glucose tests

Urine glucose tests are helpful for initial screening but have several drawbacks.

These limitations include:

• They do not provide exact blood glucose levels, only indicate if levels were high in the past.
• There's a time lag in detecting glucose in urine, as it only appears after exceeding the renal threshold.
• Individual differences in this threshold mean that the tests may not be consistent across different people.

For accurate, real-time glucose monitoring, other methods are needed.

Using biosensors to measure blood glucose

Blood glucose biosensors are a modern tool for individuals with diabetes to monitor their blood sugar levels.

Blood glucose biosensors work as follows:

1. A small blood sample from a finger prick is applied to the sensor.
2. The glucose oxidase on the strip catalyses the oxidation of glucose.
3. The hydrogen peroxide produced is then oxidised.
4. This reaction generates an electrical signal, which is proportional to the glucose concentration.
5. The glucose concentration is displayed almost instantly on a digital meter.

Biosensors offer a quick and accurate way to measure blood glucose, aiding in effective diabetes management and enabling easy data sharing with healthcare providers.