Estimation of blood glucose by Glucose oxidase method
Materials Required:
• Collection of blood sample:
About 2ml of patient’s blood should be collected by venipuncture into a tube containing a mixture of ethylenediaminetetraacetic acid and sodium fluoride in the ratio of 1:2 (W/W). Five mg of the mixture is adequate for 2ml of blood. The tube should be thoroughly shaken for complete mixing.
• Preparation of anticoagulant mixture:
100mg of EDTA and 20mg of sodium fluoride should be mixed and ground into a fine powder using a blender. This should preferably do in a fume hood. The mixture should be stored in a clean container.
Reagents:
2N Sodium hydroxide (NaOH) - 8g of NaOH is dissolve and finally make up the volume to 100ml with distilled water.
Sodium Sulphate- Zinc sulphate reagent – Dilute 55ml of the zinc sulphate solution (10g/100ml ZnSO4.7H2O) to 1 litre with the sodium sulphate solution (93mmol/liter).
Phosphate buffer 0.05M pH-7.2
Glucose oxidase reagent: Prepare this reagent fresh by dissolving 25mg of glucose oxidase and 1% ortho - toluidine in the sodium phosphate buffer. Add a small quantity of peroxidase (2mg) and makeup to 250ml with the buffer. This solution is active for about 4 weeks if stored in a brown colored bottle at 4°C.
Procedure:
• Preparation of Test: Pipette 0.1ml of blood into 1.8ml of sodium sulphate-zinc sulphate reagent in a centrifuge tube. Add 0.1ml of 2N Sodium hydroxide, centrifuge at 3000rpm for 5 minutes and take 0.5ml of supernatant in duplicate.
• Preparation of Blank: Take 0.5ml of distilled water.
• Preparation of Standard: Prepare standard concentration of glucose (200mg/dl), use 0.5ml of a range of glucose solutions (50mg/dl, 100mg/dl, 150mg/dl and 200mg/dl) suitably diluted from standard.
I. 50mg/dl - 125µl glucose standard + 375µl distilled water
II. 100mg/dl - 250µl glucose standard + 250µl distilled water
III. 150mg/dl - 375µl glucose standard + 125µl distilled water
IV. 200mg/dl - 500µl glucose standard
• Add 5ml of the glucose oxidase reagent incubate for 1h at 37°C and read the extinction at 540nm against the reagent blank.
• If the absorbance reading of the sample is too high, dilute the supernatant which was obtained earlier, 2x with distilled water and repeat the subsequent step.