A blood sugar test measures your body's ability to metabolize carbohydrates. Eating food creates a moderate increase in blood sugar levels, initiating the secretion of insulin from the pancreas to stabilize rising glucose levels. Insulin, a protein hormone, facilitates glucose absorption into the cells for energy and stores excess in the liver as glycogen. The type of blood sugar test determines the amount of preparation needed, which may or may not include fasting.
Fasting Glucose Test
When the body is in a fasting state, energy is derived from sources other than carbohydrates. Those sources include protein, fat and the glycogen stores in the liver. In response to decreased levels of carbohydrates, insulin secretion decreases. This stimulates the hormone glucagon, a protein secreted by the pancreas, to increase blood sugar. The fasting glucose test evaluates the body's ability to maintain adequate blood sugar levels within a fasting state and detect disorders of glucose metabolism. You need to fast from food and fluid for 12 hours to get accurate results, the Cleveland Clinic says.
Random Glucose Test
Random blood sugar tests require no specific preparations and no food or fluid restrictions. The purpose is to evaluate blood sugar at a particular time based on signs, symptoms or complaints of hyperglycemia or hypoglycemia. The test is frequently used in an emergency situation when symptoms such as fainting or unconsciousness result in an inability to respond to questions appropriately.
HbA1c Glucose Test
The glycosylated hemoglobin test, also called the HbA1c, is used to monitor the long-term response to diabetes therapy -- whether treatment includes oral hypoglycemics or insulin or a combination. The test reflects the average blood sugar level for the previous two to three months. Preparation for the test has restrictions on foods, fluids or medications. The HbA1c has distinct advantages, including less blood sampling occasions and results that reflect blood sugar levels over several months, the Cleveland Clinic says.
Postprandial Glucose Test
According to Lab Test Help, the postprandial glucose test is usually carried out two hours after the person consumes a meal high in carbohydrates. The purpose is to calculate the body's insulin reaction to carbohydrate ingestion, which peaks about two hours after the carbohydrate meal challenge. Preparation for the test requires consuming a balanced meal including at least 100g carbohydrates, followed by a blood sample collected two hours later. Test results vary according to the person's age.
