Measuring blood glucose levels is primarily used to diagnose and monitor diabetes and hypoglycemia.
In an individual with the signs and symptoms of diabetes, blood sugar levels above 11.1 millimoles per litre (mmol/L) are compatible with diabetes. In a patient that has been fasting for at least 8 hours, blood sugar levels equal to or higher than 7.0 mmol/L on at least two occasions also indicate that diabetes is likely. Fasting blood sugar levels between 5.6 and 6.9 mmol/L is considered pre-diabetic. These results are generally confirmed by a measurement of glycated hemoglobin (HbA1c) which is also expected to be high. Other conditions that can lead to too much glucose: acromegaly, due to a pituitary gland tumour, acute stress, chronic kidney disease, overactive adrenal glands (Cushing syndrome), excessive eating, hyperthyroidism, etc.
Abnormally low blood glucose levels (hypoglycemia) can be encountered with adrenal gland failure, excessive alcohol consumption, severe liver disease, underactive pituitary gland or thyroid, severe cardiac failure, chronic kidney failure, an overdose of insulin or a tumour producing insulin (insulinoma), prolonged fasting or the deliberate use of blood glucose lowering substances.