 Throughout a 24‑hour period blood plasma glucose levels are generally maintained between 4–8 mmol/L (72 and 144 mg/dL).Although 3.3 or 3.9 mmol/L (60 or 70 mg/dL) is commonly cited as the lower limit of normal glucose, symptoms of hypoglycemia usually do not occur until 2.8 to 3.0 mmol/L (50 to 54 mg/dL).In cases of recurrent hypoglycemia with severe symptoms, the best method of excluding dangerous conditions is often a "diagnostic fast".