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Key Points
- Glucose testing is essential for individuals with diabetes symptoms, a family history of the disease, and pregnant women for gestational diabetes screening.
- The two types of glucose tests are a fasting glucose test and a two-step glucose tolerance test, both of which measure blood glucose levels.
- The tests are used to screen for diabetes, evaluate hypoglycemia, monitor diabetes treatment, and for general health screening.
- Preparation for the tests varies and the fasting glucose test requires no food or drink except water for at least 8 hours prior.
- There are minimal risks associated with glucose testing, such as bleeding, fainting, multiple punctures to locate veins, hematoma, and infection.
If your doctor has mentioned screening your blood sugar levels, you may be wondering about how to prepare for a glucose test. A glucose test (also called a glucose screening or glucose tolerance test) is a common and important test for those who have symptoms or a family history of diabetes, according to the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK). This test is also used in pregnant women to screen for gestational diabetes (a condition that causes high blood sugar levels during pregnancy). Below you will find how to prepare for a glucose test, including what to do before, during, and after your test.
There are two types of glucose tests, according to the NIDDK—a fasting glucose test and a two-step glucose tolerance test. They note that a fasting glucose test requires you to avoid eating or drinking anything but water for at least 8 hours before the test. If your fasting glucose test indicates that you may have diabetes, a glucose challenge test can be used to confirm the results. A blood glucose tolerance test is also commonly recommended as a screening test for gestational diabetes. The glucose challenge test is done in two steps:
- Consume a sugary liquid (sometimes referred to as "Glucola")
- Wait for a certain amount of time (at least an hour)
How Do Glucose Tests Work?
Glucose tolerance tests work by measuring the level of glucose in your blood. According to the NIH, there are different methods for conducting glucose tests—either by using a small drop of blood with a glucose meter or a laboratory blood test.
A common method of blood glucose testing involves pricking the finger to obtain a small blood sample, which is then placed on a test strip and inserted into a glucose meter. The meter measures the amount of glucose in the blood sample and provides a digital readout of the results within a few seconds, according to the American Diabetes Association (ADA). Another method for testing your blood glucose level is by getting your blood drawn. This is usually done at a doctor’s office or laboratory, according to the ADA.
Another screening test that can be done is a Hemoglobin A1C test. This is a blood test that shows the average of your blood glucose levels over the past three months.
Why Are Glucose Tests Done?
Glucose tests are done to measure the level of glucose (sugar) in the blood. These tests are commonly used as a diabetes screening test for people who have symptoms of diabetes or are at a high risk of developing diabetes. Additionally, blood glucose tests may be conducted to evaluate hypoglycemia (a condition that causes low blood sugar levels), monitor your diabetes treatment, or as part of a general health screening. Glucose tolerance tests are also recommended for all pregnant women by the American Academy of Gynecologists and Obstetricians. According to the American College of Obstetricians and Gynecologists (ACOG), glucose tolerance tests are recommended between 24 and 28 weeks of pregnancy but may be done earlier if a woman has a history of gestational diabetes mellitus.
The results of your blood glucose testing can provide valuable information about your overall health and help your healthcare provider make informed decisions about your care. If you are at a higher risk of developing diabetes, your healthcare provider may recommend getting a diabetes screening. Risk factors, according to the ADA, include:
- Having a lack of physical activity in your lifestyle
- Having a high body mass index (>30)
- Having a family history of diabetes
- Certain ethnicities (African American, Hispanic, American Indian, or Asian American)
- History of gestational diabetes in past pregnancies or previously having a baby that weighed more than 9 pounds at birth
- Being pregnant at age 35 or older
- Certain medical conditions, such as metabolic syndrome or polycystic ovary syndrome
Preparing For Glucose Tests
Preparing for your glucose test depends on which type of glucose test you are having done. A screening test that measures fasting blood glucose will require you to avoid eating or drinking anything but water, for example. The preparation steps listed below are typical, according to the NIH—but it is important to follow any specific instructions provided by your healthcare provider.
Preparing for a 1-Hour Glucose Test
A 1-hour glucose test is usually used as a first-line test for people who have an increased risk of type 2 diabetes or gestational diabetes. According to the NIH, there is no specific preparation needed for the 1-hour glucose test. When you arrive for your test, you will have to drink a liquid that contains glucose (usually called “Glucola”). 1 hour after you drink the Glucola, you will have your blood drawn to assess your blood sugar levels.
Preparing for a 3-Hour Glucose Test
3-hour glucose testing is usually recommended if you had a result that was out of range in a previous test or certain risk factors. This test takes a little more preparation, according to the NIH:
- Do not eat or drink anything (other than water) for 8 to 14 hours before your test.
- Drink a glucose drink that contains approximately 100 grams of glucose
- You will have blood drawn before you drink the liquid, and again 3 more times (every 60 minutes) after you drink it.
Each time you get your blood drawn, the laboratory or healthcare provider will make a note of your blood glucose level. This test will tell your healthcare provider how your blood sugar levels are over a period of time.
Potential Downsides Of Glucose Tests
There is very little risk involved with getting a diabetes screening, according to the NIH. They note that there is a small risk associated with having your blood drawn and that some people may be more prone to feel discomfort than others.
The NIH notes that risks associated with having blood drawn are small, but may include:
- Bleeding
- Fainting or feeling lightheaded
- Multiple punctures to locate veins
- Hematoma (blood buildup under the skin)
- Infection (there is a slight risk of this any time the skin is broken)
The NIH notes that overall the risks associated with high blood sugar levels from undiagnosed diabetes are far higher than the risks associated with the test itself. Undiagnosed gestational diabetes increases several risks to your pregnancy, including preterm birth, having a large baby, and having a baby with abnormal blood glucose levels.
Foods to Eat Before A Glucose Test
Before getting a blood glucose test, you’ll want to eat foods that help keep your blood sugar stable. According to the NIH, foods that are low carb or have healthy, complex carbs are a great choice. Foods that are higher in fiber are also a good choice. Examples of healthy carbs and higher-fiber foods include:
- Whole grains (like whole wheat bread and oatmeal)
- Non-starchy vegetables like tomatoes, cucumbers, broccoli, leafy greens and green beans
- Fresh fruit like berries, apples, bananas, oranges, and melons
- Legumes like chickpeas, beans, and lentils
Adding protein-filled foods to your diet will also help stabilize your blood sugar and curb hunger. Examples of high-protein foods include low-fat dairy products, nuts, fish, or lean meat like chicken.
Foods to Avoid Before A Glucose Test
Before a glucose test, it is generally recommended that you avoid consuming certain foods that can significantly impact blood glucose levels. This includes foods high in refined carbohydrates and sugary foods (such as baked goods, candies, sugary drinks, and fruit juices). Additionally, the NIH notes that you should avoid high-carbohydrate meals and snacks, as well as alcohol, before your screening.
Following these food restrictions can ensure that your diabetes screening provides an accurate reflection of your body's glucose levels. Your healthcare provider may give you more specific guidelines, based on your individual needs.
You may be able to get a glucose tolerance test at urgent care. Find an urgent care near you with Solv.
Frequently asked questions
What happens if you drink water before a glucose test?
According to the Cleveland Clinic, drinking water can help to lower your blood glucose levels. Drinking large quantities of water right before your screening test may affect the results. However, they also note that drinking water is important for hydration and can help make your blood draw easier. Drinking sips of water before your screening tests is fine, but be sure not to drink flavored water as these can have sugar that may affect your results.
Do I need to prepare for a 1-hour glucose test?
According to the NIH, there is no specific preparation needed for a 1-hour glucose test. This means that you can eat and drink as normal.
Is coffee OK before the glucose test?
The Cleveland Clinic notes that you should avoid drinking coffee before your glucose screening test. This is because coffee contains caffeine which is a diuretic and can remove water from your body. They recommend that you drink only plain water if you are thirsty, and plan to grab your usual morning cup of coffee after your screening test.
Can you brush your teeth before the 3-hour glucose test?
According to womans.org, You can brush your teeth before the 3-hour glucose test, and any diabetes screenings (including ones you need to fast for).
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