How long do you fast before glucose test

Q: What happens if I dont fast before a blood glucose test?

What happens if I dont fast before a blood test? If you dont fast before a test that requires it, the results may not be accurate. If you forget and eat or drink something, call your doctor or lab and ask if the test can still be done. They can then tell you if you need to reschedule your test.

The purpose of the oral glucose tolerance test is to measure the body’s ability to use a type of sugar, called glucose. Glucose is the body’s main source of energy. An OGTT can be used to diagnose prediabetes and diabetes. An OGTT is most commonly done to check for diabetes that occurs with pregnancy, called gestational diabetes.

Table of Contents Show

How To Prepare – 1 hour test
How to Prepare – 3 hour test
What Tests Do I Fast For?
Why Do I Have to Fast?
What If I Slip Up?
When Can I Eat or Drink Again?
How long do you fast for pregnancy glucose test?
How long should you not eat before glucose test?
What happens if I don't fast before a blood glucose test?
Is 7 hours of fasting enough for blood test?

How To Prepare – 1 hour test

Eat a meal low in carbohydrates before this test. Example of foods to eat for breakfast would be eggs, cheese, bacon and or sausage. Avoid breads, cereals and fruit juices. Example of foods for lunch would be lettuce/salad with any kind of meat. Green beans, broccoli and any leafy vegetable. Avoid fried foods, no bread, soft drinks with sugar or sweet tea.
1 1/2 – 2 hours after eating, drink the entire 59 gram glucola drink.
Be at the office 30 minutes after finishing the cola. This is to insure that you are at the clinic on time for your blood work which will be drawn 1 hour after drinking the cola.
When you check in at the fron desk, be sure and tell the receptionist what time you finished drinking the cola.

How to Prepare – 3 hour test

If your doctor would like to see additional testing, based on your results from the 1 hour test, you may be asked to have a 3 hour OGTT. It is important to follow all of the instructions very carefully, as it will affect the results of the test.

When you arrive at the office a sample or baseline glucose test will be run and used for comparing other glucose values. You will be asked to drink a sweet liquid containing a measured amount of glucose, it is best to drink it quickly. Then blood samples will be collected at timed intervals of 1,2, and 3 hours after you drink the glucose.

Here is the best method of preparation:

Eat a balanced diet that contains at least 150 grams of carbohydrates per day for 3 days before the test. Fruits, breads, cereal, rice, crackers, and starchy vegetables such as potatoes, beans and corn are good sources of carbohydrates.
Do not eat, drink, smoke, or exercise strenuously for at least 8 hours before your first blood sample is taken.
Tell your doctor about all prescription and nonprescription medicines you are taking. You may be instructed to stop taking certain medicines before the test.
The OGTT may take up to 4 hours. Since activity can interfere with test results, you will be asked to sit quietly during the entire test. Do not eat during the test. You may drink only water during this time.

It's the morning of your bloodwork and your doctor said to fast before the test. But your stomach is growling and you have serious caffeine withdrawal hours before you roll up your sleeve. A bite of toast and a few gulps of coffee won't really make a difference, right?

Not so fast. Your results could come back wrong if you give in to temptation.

Fasting means you don't eat or drink anything but water usually for 8 to 12 hours beforehand.

If your appointment is at 8 a.m. and you're told to fast for 8 hours, only water is OK after midnight. If it's a 12-hour fast, avoid food and drink after 8 p.m. the night before.

You also shouldn't smoke, chew gum (even sugarless), or exercise. These things can rev up your digestion, and that can affect your results.

Take your prescription medications unless your doctor tells you to skip them. But ask your doctor before you take any over-the-counter drugs.

What Tests Do I Fast For?

Blood tests help doctors check for certain health problems and find out how well your body is working. Doctors also use them to figure out how well treatments are working. You don't need to fast before all blood tests. Your doctor will tell you if you need to.

These tests typically require fasting:

Fasting blood glucose measures the amount of glucose (sugar) in your blood to test for diabetes or prediabetes.
Typical fasting time: At least 8 hours
Lipid profile checks the level of cholesterol and other blood fats, like triglycerides. High levels put you at risk for developing heart disease or having a stroke. Not all situations require fasting. You may not need it if you’re younger than 25 or if you require only a partial lipid panel or if your doctor is looking for a “non-fasting” result. Ask your doctor if you need to fast for your test.
Typical fasting time: 9-12 hours
Basic or comprehensive metabolic panel is often part of a routine physical. The tests check your blood sugar, electrolyte and fluid balance, and kidney function. The comprehensive test checks your liver function, too.
Typical fasting time: 10-12 hours
Vitamin B12 test measures how much of the vitamin is in your blood. It can help diagnosis a specific type of anemia and other problems. Some medications can interfere with this test. Tell your doctor about all the drugs you take.
Typical fasting time: 6-8 hours
Iron tests are used to see if iron levels in your system are too low or too high.
Typical fasting time: 12 hours
Gamma-glutamyl transferase (GGT) shows the level of the GGT enzyme in your system. A high reading may indicate liver disease, bile duct problems, or alcohol abuse.
Your doctor may ask you to fast for at least 8 hours beforehand. You also may need to avoid alcohol and some prescription drugs the day before the test because they can affect GGT levels. Talk to your doctor before stopping any prescribed medicines.

Why Do I Have to Fast?

Nutrients in food and drinks go into your bloodstream and can change things measured by the tests, skewing your results.

For instance, if you eat or drink before a fasting blood glucose test, your blood sugar probably will be higher than if you hadn't had anything. When you're fasting, doctors get a baseline result so tests can be compared to give a true picture of your sugar levels over time.

What If I Slip Up?

If you make a mistake and eat or drink anything besides water, tell the person taking your blood. Your doctor will want to know so they can interpret your tests correctly. For the best results, they may ask you to reschedule.

When Can I Eat or Drink Again?

As soon as your blood is taken, your fast is over. You might want to bring a snack and a drink with you so you can eat as soon as possible after the test.

How long do you fast for pregnancy glucose test?

DO NOT eat or drink anything (other than sips of water) for 8 to 14 hours before your test. (You also cannot eat during the test.) You will be asked to drink a liquid that contains glucose, 100 grams (g) . You will have blood drawn before you drink the liquid, and again 3 more times every 60 minutes after you drink it.

How long should you not eat before glucose test?

You should eat your normal diet prior to the day of testing. Do not eat, drink, smoke, or exercise for at least 8-12 hours before your first blood sample is taken. You may drink plain water but no other beverages. This test may take up to four hours to complete.

What happens if I don't fast before a blood glucose test?

What happens if I don't fast before a blood test? If you don't fast before a test that requires it, the results may not be accurate. If you forget and eat or drink something, call your doctor or lab and ask if the test can still be done. They can then tell you if you need to reschedule your test.

Is 7 hours of fasting enough for blood test?

How long should you fast before a blood test? The amount of time you need to fast for will vary depending on the test. For most tests, you will be told not to consume anything but water for eight hours leading up to the test. For a few tests, a 12-hour fast may be needed.