A glucose test is a type of blood test used to determine the amount of glucose in the blood. It is mainly used in screening for any prediabetes or diabetes. Patients are instructed not to consume anything but water during the fasting period. Caffeine will also distort the results. If you eat during the period in which you are supposed to have been fasting then you would show blood sugar levels that would cause your doctor to think you have diabetes. In people already having diabetes, blood glucose monitoring is used with frequent intervals in the management of the condition.
There are several different kinds of glucose tests:
- Fasting blood sugar (FBS), fasting plasma glucose (FPG): 12 hours after eating
- Postprandial glucose test (PC): 2 hours after eating
- Glucose tolerance test: continuous testing
- Random glucose test
Reference ranges 
Fasting blood sugar 
A range of 4 to 7 mmol/l (72 to 126 mg/dl) before a meal is normal. Continual fasting levels of 5.5 to 7 mmol/l (101–125 mg/dl) causes concern of possible prediabetes and may be worth monitoring. 7 mmol/l (126 mg/dl) and above means a risk of diabetes.
Postprandial glucose 
A level of < 10 mmol/l (180 mg/dl) 90 minutes after a meal is normal.
See also 
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