Urine Analysis

What can be clinically used to measure glucose concentration in blood and urine

Dipsticks or Biosensors

What is contained on the dipstick (3)

• Two immobilised enzymes:

  • Glucose oxidase

  • Peroxidase

• Chromogen - colourless hydrogen donor

What happens when the dipstick is dipped in urine

Any glucose is present is oxidised by glucose oxidase to gluconic acid and hydorgen peroxide

What is the role of glucose oxidase

Oxidises glucose to gluconic acid and hydrogen peroxide

What is the role of peroxidase

It reduces the hydrogen peroxide formed from the oxidation of glucose forming water and oxygen

What causes the chromagen to change colour

It gets oxidised

How does the glucose concentration affect the colour change

The more glucose present, the more chromagen is oxidised and the darker the colour

Why can a dipstick be considered semi-quantitative

As the colour produces can be compared to a colour chart in oder to estimate the quantity of glucose present.

How do biosensors work

• contains immobilised glucose oxidase

• Enzyme held between to membranes positioned at the tip of a platinum electrode

• Electrode placed in a drop of blood

• Glucose oxidase reacts with glucose in drop of blood to produce gluconic acid and hydrogen peroxide

• Hydrogen peroxide is oxidised at the platinum electrode which generates electric current detected by the electrode

How is a numerical value obtained from the biosensor

• when the hydrogen peroxide is oxidised at the platinum electrode an electric current, detected by the electrode

• The size of the current is proportional to the concentration of glucose in the patient’s blood

• A digital read out gives a numerical reading of blood glucose concentration.

• The reading is quantitative, gives actual value of blood glucose concentration.

What are the advantages of a biosensor.

• does not involve colour matching, which is subjective and there is no need to interpret a colour chart

• Biosensors can be used repetitively.