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A blood glucose test measures the amount of a type of sugar, called glucose, in your blood. Glucose comes from carbohydrate foods. It is the main source of energy used by the body. Insulin is a hormone that helps your body's cells use the glucose. Insulin is produced in the pancreas and released into the blood when the amount of glucose in the blood rises.
Normally, your blood glucose levels increase slightly after you eat. This increase causes your pancreas to release insulin so that your blood glucose levels do not get too high. Blood glucose levels that remain high over time can damage your eyes, kidneys, nerves, and blood vessels.
There are several different types of blood glucose tests.
To make a diagnosis of type 2 diabetes, your doctor will use the American Diabetes Association's criteria.
Blood glucose tests are done to:
This is one of several tests that is used to diagnose diabetes. For a fasting blood sugar test, do not eat or drink anything other than water for at least 8 hours before the blood sample is taken.
If you have diabetes, you may be asked to wait until you have had your blood tested before taking your morning dose of insulin or diabetes medicine. You may have a random blood sugar test instead, which will not require an 8-hour fast.
For a 2-hour postprandial test, start eating a meal exactly 2 hours before the blood sample is taken. A home blood sugar test is the most common way to check 2-hour postprandial blood sugar levels.
No special preparation is required before having a random blood sugar or A1c test.
For an oral glucose tolerance test, you'll need to follow a special diet for 3 days before the test. And do not eat, drink, smoke, or exercise strenuously for at least 8 hours before your first blood sample is taken.
To learn more about how to prepare for this test, see Oral Glucose Tolerance Test.
Talk to your doctor about any concerns you have regarding the need for the test, its risks, how it will be done, or what the results may mean.
To help you understand the importance of this test, fill out the medical test information form( What is a PDF document? ).
The health professional taking a sample of your blood will:
The blood sample is taken from a vein in your arm. An elastic band is wrapped around your upper arm. It may feel tight. You may feel nothing at all from the needle, or you may feel a quick sting or pinch.
There is very little risk of a problem from having blood drawn from a vein.
A blood glucose test measures the amount of a type of sugar, called glucose, in your blood.
Results are often ready in 1 to 2 hours. Glucose levels in a blood sample taken from your vein (called a blood plasma value) may differ a little from glucose levels checked with a finger stick.
Each lab has a different range for what's normal. Your lab report should show the range that your lab uses for each test. The normal range is just a guide. Your doctor will also look at your results based on your age, health, and other factors. A value that isn't in the normal range may still be normal for you.
Many conditions can change your blood glucose levels. Your doctor will discuss any significant abnormal results with you in relation to your symptoms and past health.
You may have diabetes. To make a diagnosis of type 2 diabetes, your doctor will use the American Diabetes Association's criteria.
Other conditions that can cause high blood glucose levels include:
A fasting glucose level below 40 mg/dL (2.2 mmol/L) in women or below 50 mg/dL (2.8 mmol/L) in men that is accompanied by symptoms of hypoglycemia may mean you have an insulinoma, a tumor that produces abnormally high amounts of insulin.
Low glucose levels also may be caused by:
Reasons you may not be able to have the test or why the results may not be helpful include:
Current as ofApril 16, 2019
Author: Healthwise StaffMedical Review: E. Gregory Thompson MD - Internal MedicineKathleen Romito MD - Family MedicineAdam Husney MD - Family MedicineMatthew I. Kim MD - EndocrinologyDavid C.W. Lau MD, PhD, FRCPC - Endocrinology
Current as of:
April 16, 2019
Medical Review:E. Gregory Thompson MD - Internal Medicine & Kathleen Romito MD - Family Medicine & Adam Husney MD - Family Medicine & Matthew I. Kim MD - Endocrinology & David C.W. Lau MD, PhD, FRCPC - Endocrinology
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