Fasting vs Nonfasting Blood Sugar
The main energy source consumed by humans in everyday life is carbohydrates, and they are then converted into simple sugars like glucose. The production of energy is thus, dependent on the level of glucose in the blood, and different types of hormones are also facilitating the blood levels of glucose. Hormones like insulin are present when there are adequate levels of blood glucose and help to store it as glycogen and fat, in the muscle tissues, and liver. However, at times of poor food intake, hormones like glucagon and cortisol help produce new glucose from non carbohydrate materials (gluconeogenesis) and through the breakdown of glycogen (glycogenolysis). Levels of blood sugar are thus variant upon different factors of food intake, the time from the last meal, and concurrent diseases and medications. Here, we will elaborate on two main glucose levels, which is the fasting glucose level and the non-fasting glucose level.
Fasting Blood Sugar
Fasting blood sugar is taken as the venous blood sugar level expected to see in a patient who had fasted for about 8-12 hours. The normal value of this test is below 100mg/dl. This value is dependent on the body insulin levels, and the peripheral utilization of glucose. Even in times of fasting, if there is reduced bodily insulin and poor peripheral utilization, the patient would have diabetes mellitus. This is the benchmark test of diagnosis of DM, and treatment can be started with one abnormal value with symptoms or two abnormal values. The only problem with this test is the difficulty in doing the test quickly.
Non-Fasting Blood Sugar
Non-fasting blood sugar denotes the usual random blood sugar or the postprandial blood sugar. Here, the time of the last meal is not sure or usually 2 hours after the last meal. In this, the value can go high according to the meal in the first hour following the meal, or would be below 144 mg/dl at 2 hours after the last meal. Here, an active effort has not been taken to fast, and the value is dependent on the time lapsed from the last meal, the type of the meal, and previous factors. Thus, this test is ideal to monitor drug usage and dietary modifications following the diagnosis of DM. This test is easy to do, and capillary measurements can also be done, but would need to reduce 18 mg/dl to convert to the venous values.
What is the difference between Fasting Blood Sugar and Non-Fasting Blood Sugar?
FBS and RBS/PPBS differ on the values of cut off, the ability to conduct the test quickly, and the utility of the test in diagnosis or management of the disease condition.
• Both the tests measure the venous blood glucose levels. Thus, both can give an indication as to the level of control of the blood glucose values.
• Fasting values need a fast of up to 8-12 hours, whereas non-fasting values need only up to 2 hours.
• FBS value is dependent on the insulin level and peripheral activity. However, the non-fasting values, or RBS/PPBS is dependent on the meal and the drug use for diabetes, as well.
• Thus, FBS is a reliable diagnostic tool, whereas RBS/PPBS are reliable monitoring tools.
• FBS is cumbersome to do, whereas RBS/PPBS can be done at the consultation itself.