What is Fasting Plasma Glucose?

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  • Written By: Helga George
  • Edited By: Michelle Arevalo
  • Last Modified Date: 24 September 2019
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Fasting plasma glucose (FPG) is the level of sugar in the blood after someone has not eaten for a prolonged period of time, usually overnight. It is often used as a measure of how well people with diabetes are controlling their blood sugar. These levels can be too high — a possible indication that the person suffers from pre-diabetes or diabetes. They can also be too low, which is known as hypoglycemia and is frequently a side effect of insulin usage.

Diabetes is a syndrome of diseases that share abnormalities in the processing of carbohydrates. Type I diabetics have an autoimmune disease that affects the pancreas. They produce little or no insulin. These patients either have an automatic pump that provides insulin as needed, or they must inject it themselves before eating. Such individuals must perform a fasting plasma glucose test several times a day, with a home blood sugar meter, to know how much insulin to administer.

Type 2 diabetes is a different disorder, in which sugar builds up in the blood because the cells lose the ability to react to insulin. There is a strong genetic component to this disease, but it is also often associated with obesity. Lifestyle changes, such as increased exercise and loss of excess weight, can often help to lower fasting plasma glucose levels.


It is generally not necessary for Type 2 diabetics to check their blood sugar levels daily. A FGP test is often the first thing that many patients do upon rising for the day, however. Closely monitoring fasting plasma glucose levels can help to determine whether exercise or medications are working properly. Health professionals generally want to see logs of FGP tests during appointments.

Fasting plasma glucose tests are also important for individuals with pre-diabetes. This is because they are at increased risk of developing Type 2 diabetes. They usually need to frequently monitor their blood sugar levels to ensure that they have not developed the disorder.

Ideal fasting plasma glucose levels range from 80-100 mg/dL (4.5-5.7 mmol/L). Levels that persist over 230 mg/dL (13 mmol/L) indicate that one should seek medical attention. Typically, blood sugar levels of 126 mg/dL (7.1 mmol/L) or higher are used as part of a diabetes diagnosis. Levels that range between 100 and 126 mg/dL (4.5-7.1 mmol/L) suggest that an individual has pre-diabetes.

Alternatively, fasting plasma glucose levels that are lower than 70 mg/dL mean that a person has hypoglycemia. This condition can be dangerous, and can cause coma and even death. It should be treated immediately with glucose tablets or food that has a high level of sugar. Hypoglycemia is more frequently a problem for Type 1 diabetics, because it can be a frequent side effect of insulin injection.

Blood sugar levels can fluctuate over the course of the day. A more reliable test is the hemoglobin A1c test. It measures the amount of the blood protein hemoglobin with sugar bound to it. This measurement gives an estimate of the blood sugar levels over the last three months. This test must be performed by a laboratory, and cannot be done at home.


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