Things to Know Before Taking a Fasting Plasma Glucose Test (2022)

The fasting plasma glucose (FPG) test, also known as the fasting blood glucose test (FBG) or fasting blood sugar test, measures the levels of glucose (sugar) in the blood. Used to screen for diabetes, it is a relatively simple, accurate, and inexpensive test that exposes problems with insulin functioning.

Things to Know Before Taking a Fasting Plasma Glucose Test (1)

Purpose of Test

The FPG test is recommended as a screening test for people 35 or older to be repeated every three years. It may also be used outside of those parameters for people who have symptoms of diabetes or multiple risk factors for diabetes.

Prolonged fasting triggers a hormone called glucagon, which is produced by the pancreas and causes the liver to release glucose (blood sugar) into the bloodstream. If you don’t have diabetes, your body reacts by producing insulin, which prevents hyperglycemia (high blood sugar). However, if your body cannot generate enough insulin or cannot appropriately respond to insulin, fasting blood sugar levels will stay high.

Lack of insulin or insulin resistance causes higher than normal levels of glucose in the blood.Things to Know Before Taking a Fasting Plasma Glucose Test (2)

In the diagnosis of diabetes, the FPG test may be performed alone or along with one of these other assays:

  • Random glucose tolerance test
  • Oral glucose tolerance test (OGTT), which measures blood glucose levels after the ingestion of a highly-sugared beverage following a period of fasting
  • Hemoglobin A1C, a measurement of average blood glucose levels over the course of two or three months

If your healthcare provider is recommending the FPG test because you've been having symptoms of diabetes, you can expect it will need to be repeated on a different day to confirm the results. Or, your healthcare provider may recommend the OGTT or the hemoglobin A1C test instead of a second FPG test.

The FPG test is regarded as accurate and more sensitive than the A1C, though it is not quite as sensitive as the gold standard of glucose tests, the OGTT.

A key difference between the FPG test and the OGTT is the OGTT cannot be used to monitor or measure the effectiveness of a diabetes management program in those who have already been diagnosed with the disease.

Risks and Contraindications

As a standard blood draw performed in a lab, the FPG test is considered safe outside of a handful of potential risks associated with any blood work:

  • Multiple venipuncture wounds if the technician has trouble locating a vein
  • Excessive bleeding
  • Dizziness, lightheadedness, or fainting
  • Bruising or the accumulation of blood under the skin (hematoma)
  • Infection

Before the Test

Once your healthcare provider orders an FPG test, they should be able to let you know if you'll need to repeat the test a second time on a different day or perform an OGTT or A1C test. If you have any questions or qualms about the test, ask your healthcare provider at this time.

Timing

The FPG test requires that you be in a fasted state—having not eaten anything for at least eight hours—so the test is usually scheduled for earlier in the morning. Once the lab technician is prepped to draw your blood, the test takes all of five minutes.

Location

The test will usually take place in a lab, hospital, or even your healthcare provider's office.

What to Wear

Short sleeves are helpful for a blood draw in your arm, but not absolutely necessary. Dress comfortably—you can always push up your shirt sleeve or remove a layer of clothing.

Food and Drink

This is a fasted test, which means no food or drink for eight to 12 hours before testing. The ideal way to prep for this is to fast overnight. An occasional sip of water is OK, but drinking a full glass is usually not allowed. Follow your healthcare provider's directions.

Cost and Health Insurance

While the price may vary depending on where the test is performed, the FPG test is not expensive. Most health insurance policies cover the FPG for routine examinations, monitoring, or for the purpose of diagnosing diabetes. You may be responsible for a co-pay or co-insurance fee. Call your insurance company to determine if you will have any out-of-pocket expenses for the test.

What to Bring

Bring your insurance card, identification, and a copy of the lab request/referral form. You might also want to bring a book or magazine in case you get stuck in the waiting room.

Some people feel woozy from having blood drawn after a long fast, due to a drop in blood sugar. If you anticipate having this reaction, bring along a snack to eat right after your test is complete.

Other Considerations

A quick web search will bring up numerous FPG testing kits you can order at home. While these may be helpful for monitoring diabetes after it's been diagnosed, they are not recommended for diagnosing or screening for diabetes.

During the Test

Your blood sample will be taken by a lab technician, nurse, or phlebotomist (a person trained in venipuncture).

(Video) What is meant by Fasting Blood Sugar Test & when is it done? - Dr. Samit Thakur

Pre-Test

Once you arrive, check in at the front desk. You may need to fill out insurance billing forms or consent forms. Speak up if you're nervous about having blood work done or have a history of feeling faint after medical procedures so that the lab tech or nurse can take special precautions.

Throughout the Test

The test consists of a simple, noninvasive blood test. The technician or person administering the test will collect a small vial of blood from your arm (if being used for screening or diagnosis) or a drop from a finger prick (if being used for monitoring purposes). Your blood sample will be sent to a lab for analysis.

The technician will ask you which arm you prefer to use for the test—most people choose their non-dominant arm. You'll be seated, with your chosen arm resting on a flat surface. If necessary, roll up your sleeve above your elbow. The technician will place a rubber band as a tourniquet just below your bicep in order to find a vein in the crook of your arm. They will clean the area with an alcohol wipe and press a small, fine needle into your vein: You may feel some pain for a brief moment.

Blood will start to collect into a vial, at which time the technician will remove the tourniquet to encourage more blood flow. Tell the technician if you start to feel woozy or lightheaded. It can help to look away from the blood collection if necessary.

The needle will be removed from your arm and the technician will place a cotton ball or cotton gauze square over the puncture site to stop the bleeding, along with a bandage.

If instead, you're having your fasting glucose levels monitored, you may just need a finger prick in the office. This point-of-care test usually gets quick results and is only slightly uncomfortable, not painful.

How to Make Blood Draws Easier

Post-Test

As long you're not feeling faint or weak, you should be free to leave as soon as the test is complete. If you're feeling dizzy, you may be asked to sit in the waiting room for a few minutes. This would be the time to have a snack to replenish low blood sugar levels as a result of fasting.

After the Test

After your blood draw, you can head home or get back to your day.

Managing Side Effects

Keep an eye on the puncture site to make sure the bleeding has stopped; note if there's any bruising, swelling, or infection. Bruising should go away on its own in a few days, but swelling and infection may require medical attention.

Interpreting Results

Depending if your test took place in your healthcare provider's office or in a lab, results may take anywhere from the same day to up to a week to arrive.

Healthcare providers interpret FPG test results by looking at glucose levels in the blood. Diagnosis categories include the following, measured in milligrams per deciliter (mg/dL).

ReadingInterpretation
70 mg/dL to 99 mg/dLNormal
100 mg/dL to 126 mg/dLPrediabetes/increased risk of diabetes
Over 126 mg/dLDiabetes
Under 55 mg/dLHypoglycemia/dangerously low

If your FPG test results are borderline or elevated and indicate diabetes, the test will need to be repeated a second time in the near futureor other tests might be performed, such as the hemoglobin A1C test,oral glucose tolerance test, or the postprandial plasma glucose test.

Results may vary from lab to lab—or even in the same lab—from day to day. As a result, two abnormal results from tests taken on two different days are required to confirm a diagnosis.

Results may be lower if blood is drawn in the afternoon rather than in the morning. A glucose level sometimes can be falsely low if too much time passes between when the blood is drawn and the lab processes the sample. The results can also be affected by previous or current medical conditions or by personal habits, such as smoking and exercise.

Abnormal test results may also indicate diabetes. A healthcare professional should consider a person’s full medical history when conducting this test and interpreting the results. Keep in mind that this blood test is used not only to diagnose diabetes but also to prevent it. Higher values are likely to reflect diet and lifestyle issues as well as poor insulin functioning.

Follow Up

Depending on your confirmed results, there are several courses of action.

High FPG and Symptoms of High Blood Sugar

If you are experiencing symptoms of elevated blood sugar and your FPG reading is above 126 mg/dL, that may be enough evidence for your healthcare provider to confirm your diagnosis of diabetes.

In that case, you and your healthcare provider will discuss setting up a treatment plan. Depending on the type of diabetes you have, it may include regular glucose monitoring, medication, and supplements, along with lifestyle changes, such as a whole foods, low-carb diet, exercise, and stress reduction practices.

There are several reasons for having a high FPG that may not be due to diabetes:

(Video) What is the difference between A1c and Fasting Blood Glucose Testing?

  • Cushing's syndrome
  • Preeclampsia
  • Pancreatitis
  • Sepsis
  • Myocardial infarction (heart attack)

Your healthcare provider will be able to track your symptoms and perform more tests to rule these other conditions out if necessary.

Borderline/Prediabetes

If instead, your FPG reading is between 100 mg/dL to 126 mg/dL, the American Diabetes Association recommends regular screening for diabetes be repeated yearly. Having prediabetes doesn't mean you'll automatically develop type 2 diabetes, however. Prediabetes (and type 2 diabetes, for that matter) are reversible conditions.

What Are Tests for Prediabetes?

Low FPG and Symptoms of Low Blood Sugar

An FPG reading below 55mg/dL in a person without diabetes is considered hypoglycemia; the cutoff for people with diabetes is below 70mg/dL

If your FPG reading is below 70 mg/dL, this is indicative of hypoglycemia and could mean you've developed one of the following conditions:

  • Reactive (postprandial) hypoglycemia
  • Kidney or liver insufficiency
  • Pancreatic tumors like insulinomas (if FPG is below 55mg/dL and symptoms are present)
  • Hypopituitarism, a rare disorder characterized by inadequate production of hormones
  • Malabsorption syndrome

These conditions will also require further testing and symptom tracking by your healthcare provider.

Monitoring

Depending on your results, if you're using the FPG test to monitor your fasting glucose levels, your healthcare provider may want to adjust your medication or treatment plan according to how your levels present.

Other Considerations

If you're diagnosed with diabetes based on confirmed readings from an FPG test, your healthcare provider will then attempt to define which type.

  • Type 1 diabetes is an autoimmune condition in which the pancreas may no longer be producing insulin. Additional tests may be required to check for autoimmune antibodies, such as the C-peptide test.
  • Type 2 diabetes is a chronic disease in which the body becomes insulin resistant and can no longer efficiently process sugar for energy.
  • Gestational diabetes occurs during pregnancy.

Whether a person has type 1, type 2, or gestational diabetes, a healthy lifestyle helps insulin to work better. In this sense, the fasting plasma glucose test is a signal for action, not necessarily a cause for anxiety.

Keep an open dialogue with your healthcare provider about your results from the FPG test and what steps you should take next.

Understanding Type 1 Diabetes

A Word From Verywell

The fasting blood glucose test is a noninvasive blood test that can be used to determine diabetes risk, diagnose diabetes, and evaluate blood sugar and insulin function in those people who have diabetes. Abnormal results can help guide you to make lifestyle changes and determine medication adjustments if needed.

Frequently Asked Questions

  • What blood tests require fasting?

    Besides the fasting glucose plasma test, another blood test that requires fasting includes a lipid test or lipid profile. This type of test measures triglyceride and cholesterol levels in the blood to assess the risk of heart disease. It can tell you the levels of "good" cholesterol (HDL) and "bad" cholesterol (LDL) in your blood.

    (Video) Blood Sugar Levels Chart | Includes fasting and after eating

  • What is a random glucose tolerance test?

    A random glucose tolerance test is used to help diagnose diabetes in people experiencing symptoms of hyperglycemia or hyperglycemia crisis (a potentially serious issue in people with uncontrolled diabetes). Fasting is not required for this test, but its results may be affected by the last time a person ate food. Other tests like the A1C or glucose tolerance test may be needed depending on results.

16 Sources

Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.

  1. American Diabetes Association. 2. Classification and diagnosis of diabetes: Standards of medical care in diabetes—2022. Diabetes Care. 2022;45(Supplement 1):S17-S38. doi:10.2337/dc22-S002

  2. American Diabetes Association. Hypoglycemia (Low Blood Sugar).

  3. American Diabetes Association. Diabetes Overview: Diagnosis.

  4. National Institute of Diabetes and Digestive and Kidney Diseases.Diabetes and Prediabetes Tests.

  5. American Diabetes Association. 6. Glycemic targets: Standards of medical care in diabetes—2022. Diabetes Care. 2022;45(Supplement 1):S83–S96. doi:10.2337/dc22-S006

  6. National Institute of Diabetes and Digestive and Kidney Diseases. Cushing's Syndrome.

  7. Hyperglycemia and Adverse Pregnancy Outcome (HAPO) Study Cooperative Research Group. Hyperglycemia and Adverse Pregnancy Outcome (HAPO) study: preeclampsia. Am J Obstet Gynecol. 2010;202(3):255.e1-7. doi:10.1016/j.ajog.2010.01.024

  8. Kikuta K, Masamune A, Shimosegawa T. Impaired glucose tolerance in acute pancreatitis. World J Gastroenterol. 2015;21(24):7367-74. doi:10.3748/wjg.v21.i24.7367

  9. Wernly B, Lichtenauer M, Hoppe UC, Jung C. Hyperglycemia in septic patients: an essential stress survival response in all, a robust marker for risk stratification in some, to be messed with in none. J Thorac Dis. 2016;8(7):E621-4. doi:10.21037/jtd.2016.05.24

  10. Ishihara M. Acute hyperglycemia in patients with acute myocardial infarction. Circ J. 2012;76(3):563-71. doi:10.1253/circj.cj-11-1376

  11. Galati SJ, Rayfield EJ. Approach to the patient with postprandial hypoglycemia. Endocr Pract. 2014;20(4):331-40. doi:10.4158/EP13132.RA

    (Video) Blood sugar test normal range

  12. Desimone ME, Weinstock RS. Non-diabetic hypoglycemia. In: Feingold KR, Anawalt B, Boyce A, et al., editors. Endotext [Internet]. South Dartmouth (MA): MDText.com, Inc.

  13. MedlinePlus. Fasting for a Blood Test.

  14. MedlinePlus. Cholesterol Levels.

  15. Van Ness-Otunnu R, Hack JB. Hyperglycemic crisis. J Emerg Med. 2013;45(5):797-805. doi:10.1016/j.jemermed.2013.03.040

  16. MedlinePlus. Blood Sugar Test.

By Debra Manzella, RN
Debra Manzella, MS, RN, is a corporate clinical educator at Catholic Health System in New York with extensive experience in diabetes care.

FAQs

What should you not do before a fasting glucose test? ›

You can eat and drink as normal before some blood tests. But if you're having a "fasting blood test", you will be told not to eat or drink anything (other than water) beforehand. You may also be told not to smoke before your test.

What are the fasting requirements when taking a fasting plasma glucose test? ›

The fasting plasma glucose test is the simplest and fastest way to measure blood glucose and diagnose diabetes. Fasting means that you have had nothing to eat or drink (except water) for 8 to 12 hours before the test.

How do you prepare a patient for a fasting blood sugar test? ›

Fasting blood sugar is a simple, common blood test to diagnose prediabetes, diabetes or gestational diabetes. Before the test, you shouldn't have anything to eat or drink (except water) for 8 to 12 hours. Talk to your healthcare provider about whether you need a fasting blood glucose test.

What should I eat the day before fasting glucose test? ›

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.

Does drinking water affect blood sugar test? ›

Drinking water before a fasting blood sugar test can actually decrease blood sugar levels, or at least prevent levels from getting too high. Water allows more glucose to be flushed out of the blood. When you're dehydrated, it means your overall blood volume is lower than normal, but your sugars will be the same.

Can I drink coffee before a fasting blood test for glucose? ›

According to a 2020 study, drinking black coffee "does not seem to alter fasting TG or markers of fat tolerance." It also does not influence fasting glucose and glycemic response. This is something to consider if you're taking a fat tolerance test or basic metabolic test.

What affects fasting blood sugar? ›

Fasting blood sugar depends on three factors: the contents of a person's last meal. the size of their previous meal. their body's ability to produce and respond to insulin.

What can cause a false high glucose reading? ›

High uric acid and low hematocrit values have been suggested to cause falsely high BG readings, thereby resulting in inappropriate therapeutic decisions.

Can I drink water before fasting blood test? ›

If your health care provider has told you to fast before a blood test, it means you should not eat or drink anything, except water, for several hours before your test. When you eat and drink normally, those foods and beverages are absorbed into your bloodstream.

What are 3 things you need to avoid while checking blood sugar with glucometer? ›

Keep your glucose meter and test strips at room temperature. Wash and dry your hands and the testing site thoroughly with soap and water before pricking your skin. Don't use hand sanitizer before testing. If using alcohol wipes, let the site completely dry prior to pricking.

How much water should you drink before a blood test? ›

Ideally, start drinking more fluids the day before your blood draw, and continue to drink water before you have your blood drawn. Excessive amounts aren't necessary; most sources ecommend that an adult drink 64 ounces of water per day for good health, which is more than adequate for having your blood drawn.

What time of day is blood sugar highest? ›

The dawn phenomenon, also called the dawn effect, is the term used to describe an abnormal early-morning increase in blood sugar (glucose) — usually between 2 a.m. and 8 a.m. — in people with diabetes.

Can I brush my teeth before a fasting blood test? ›

Yes, brushing your teeth is permitted unless otherwise indicated by your physician, assuming you do not use large amounts of toothpaste and swallow the lather.

Does what I eat the night before affect my glucose test? ›

Glucose tests come with specific instructions — such as fasting — and it's important to follow them. Changes to your diet a day or two before a glucose test won't make a huge difference to your results.

Will a banana affect a glucose test? ›

If we understand correctly, ripe bananas can contain up to 15% sugar (with about 1/2 of that as glucose). So, in theory, as the bananas ripen and the sugar content increases due to the conversion of the starch content to sugars, the test strips should be able to detect the glucose.

Does a glass of water lower blood sugar? ›

Did you know it's Sugar Free February and that drinking water can help to lower blood sugar levels by diluting the amount of glucose (sugar) in your blood stream. By drinking water lots of water you can reduce your blood sugar as it indirectly will reduce insulin resistance and help reduce hunger.

How can I lower my fasting blood sugar in the morning? ›

How can high blood sugar levels in the morning be controlled?
  1. Changing the timing or type of your diabetes medications.
  2. Eating a lighter breakfast.
  3. Increasing your morning dose of diabetes medication.
  4. If you take insulin, switching to an insulin pump and programming it to release additional insulin in the morning.
25 May 2018

How much water do you need to drink to lower blood sugar? ›

Diabetes research

Participants that consumed more than one litre of water per day had a 28 per cent lower risk of developing new onset hyperglycemia, compared to those drinking less than 500ml of water per day.

Why is my fasting glucose high in the morning? ›

The dawn phenomenon

In the early hours of the morning, hormones, including cortisol and growth hormone, signal the liver to boost the production of glucose, which provides energy that helps you wake up. This triggers beta cells in the pancreas to release insulin in order to keep blood glucose levels in check.

Will one cup of coffee affect blood test? ›

Even if you drink it black, coffee can interfere with blood test results. That's because it contains caffeine and soluble plant matter, which might skew your test results. Coffee is also a diuretic, which means that it will increase how much you pee. This can have a dehydrating effect.

How can I improve my blood test results quickly? ›

For the most accurate blood test results, your blood should be drawn when you're rested, Dr. Krajcik says. A workout before a fasting blood test can alter the results of cholesterol and glucose tests.

What drink lowers blood sugar? ›

Barley or jau water is high in insoluble fibre, which makes it good for diabetics. It is recommended for diabetics as it helps stabilise blood glucose levels. Make sure you drink unsweetened barley water to get effective results. The antioxidant properties of barley water also helps keep many diseases at bay.

Can you have high fasting blood sugar and not be diabetic? ›

Nondiabetic hyperglycemia means your blood glucose (sugar) level is high even though you do not have diabetes. Hyperglycemia may happen suddenly during a major illness or injury. Or, hyperglycemia may happen over a longer period and be caused by a chronic disease (diabetes type I or II).

Can stress raise fasting blood sugar? ›

Stress hormones have a big role to play. When you're experiencing physical or emotional stress, hormones are released that increase your blood sugar. Cortisol and adrenaline are other primary hormones involved. This is a perfectly natural response.

What can throw off a glucose test? ›

Avoid sugars and refined carbs

Don't eat high-sugar foods or simple carbs (including refined grains) the morning of your glucose screening. The body breaks these foods down quickly, leading to a spike in blood sugar levels. That means avoiding breakfast favorites like: Orange juice and other fruit juices.

Why do you need to wipe off the first blood drop? ›

Wipe away the first drop of blood because it may be contaminated with tissue fluid or debris (sloughing skin). Avoid squeezing the finger or heel too tightly because this dilutes the specimen with tissue fluid (plasma) and increases the probability of haemolysis (60).

How does squeezing finger affect blood sugar? ›

On average, blood sugar readings were lower when people put pressure on the finger. The finding, according to the researchers, is in line with advice to avoid firm squeezing of the tested finger.

Does what you eat the day before affect a fasting blood test? ›

McKnight also mentioned the food or drinks you consume the day or night before a blood test does not impact your test results, unlike what you eat or drink the morning of your test. “It's recommended that you avoid coffee and other liquids during your fast,” McKnight said.

Does 12-hour fasting mean no water? ›

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.

Does fasting longer lower blood sugar? ›

With each additional hour of fasting the blood glucose decreases by about 0.024 mmol/L (≙0.4 mg/dL) in men and 0.009 mmol/L (≙0.2 mg/dL) in women.

Which finger is best for glucose testing? ›

Recommended finger: the World Health Organisation recommends the middle or ring fingers are used for blood glucose tests (second and third fingers). You may want to avoid using your little finger due to the skin being thin.

Which hand is more accurate for blood sugar? ›

Figure 1. Differences in glucose readings of right arm from left arm over a 24-hour period. The right arm was higher 96% of the time and was half as likely to detect glucose levels outside the 70-140 mg/dL range compared to the left arm.

Which is a rule for blood glucose testing? ›

Fasting Blood Sugar Test

A fasting blood sugar level of 99 mg/dL or lower is normal, 100 to 125 mg/dL indicates you have prediabetes, and 126 mg/dL or higher indicates you have diabetes.

How long does it take water to hydrate your veins? ›

It can take just 5 minutes to begin rehydrating your body. On the other hand, if you drink water while eating, your body will prioritize digesting food before water. This often takes up to 120 minutes to digest water and rehydrate your body.

What medications should you not take before a blood test? ›

Certain prescription and over-the-counter medications can impact the results of your blood test.
...
Examples of medicine that could skew your lab test results include:
  • Vitamins (for example, Biotin)
  • Antibiotics.
  • Antidepressants.
  • Steroids (like Prednisone)
  • Acetaminophen.
  • NSAIDs.
9 Aug 2022

How long does it take for water to get to your veins? ›

Liquids are rapidly absorbed into the bloodstream, and fluids in excess of the body's needs are eliminated via the kidneys as urine, much faster. Water absorption can occur as soon as 5 minutes after ingestion and peaks around 20 minutes after ingestion.

Does caffeine raise blood sugar? ›

For most young, healthy adults, caffeine doesn't appear to noticeably affect blood sugar (glucose) levels, and having up to 400 milligrams a day appears to be safe.

What foods can lower blood sugar quickly? ›

The 17 Best Foods to Lower (or Regulate) Your Blood Sugar
  • Broccoli and broccoli sprouts. Sulforaphane is a type of isothiocyanate that has blood-sugar-reducing properties. ...
  • Seafood. ...
  • Pumpkin and pumpkin seeds. ...
  • Nuts and nut butter. ...
  • Okra. ...
  • Flax seeds. ...
  • Beans and lentils. ...
  • Kimchi and sauerkraut.
10 Aug 2020

Can being tired affect your blood sugar? ›

If you get less than 7 hours of sleep per night regularly, your diabetes will be harder to manage. Too little sleep can: Increase insulin resistance. Make you hungrier the next day and reduce how full you feel after eating.

What can you not do before a fasting blood test? ›

You can eat and drink as normal before some blood tests. But if you're having a "fasting blood test", you will be told not to eat or drink anything (other than water) beforehand. You may also be told not to smoke before your test.

What can you not eat the night before a fasting blood test? ›

If a healthcare professional has asked a person to fast, they should not consume anything other than water the night before a cholesterol test. Fasting means that a person can only consume water for the hours before their test.

Can I have water before my glucose test? ›

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 should I not do before my 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 (75 g). You will have blood drawn before you drink the liquid, and again 2 more times every 60 minutes after you drink it.

What should you not do before glucose test? ›

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 you take your morning dose of insulin or diabetes medicine.

What foods to avoid if you are prediabetic? ›

Foods to avoid if you are prediabetic include sweets (pastries, cookies, cake, candy, pie, doughnuts), refined carbohydrates (white bread, pasta, bagels, crackers, pretzels), sweetened breakfast cereals, flavored yogurt, fried foods, fatty meats, jams, jellies, potato chips, snack bars, and others.

› health › fasting-before-bloo... ›

Some blood tests will require you to fast beforehand. In these cases, your doctor will instruct you not to eat or drink anything, except water, in the hours lea...
Getting tested for diabetes? Learn how to tweak your diet for better health — and better test results.
Fasting means not eating or drinking anything, except water, for a certain period of time. Fasting before a blood test can help ensure the accuracy of certain t...

What can cause a false high glucose reading? ›

High uric acid and low hematocrit values have been suggested to cause falsely high BG readings, thereby resulting in inappropriate therapeutic decisions.

What are 3 things you need to avoid while checking blood sugar with glucometer? ›

Keep your glucose meter and test strips at room temperature. Wash and dry your hands and the testing site thoroughly with soap and water before pricking your skin. Don't use hand sanitizer before testing. If using alcohol wipes, let the site completely dry prior to pricking.

Will eating sugar the day before blood test affect results? ›

McKnight also mentioned the food or drinks you consume the day or night before a blood test does not impact your test results, unlike what you eat or drink the morning of your test.

Why do you wipe away first drop of blood for glucose test? ›

Some facilities test the first drop of blood. Others require nursing personnel to wipe away the first drop of blood with gauze, and test the second drop. The rationale for wiping away the first drop of blood is that the alcohol in the prep pad, and consequently on the fingertip, may alter values.

What can throw off a glucose test? ›

Avoid sugars and refined carbs

Don't eat high-sugar foods or simple carbs (including refined grains) the morning of your glucose screening. The body breaks these foods down quickly, leading to a spike in blood sugar levels. That means avoiding breakfast favorites like: Orange juice and other fruit juices.

What can affect glucose test? ›

Here are a few of the causes:
  • Not enough food, like a meal or snack with fewer carbohydrates than usual, or missing a meal or snack.
  • Alcohol, especially on an empty stomach.
  • Too much insulin or oral diabetes medications.
  • Side effects from other medications.
  • More physical activity or exercise than usual.

Can you have a high blood sugar and not be diabetic? ›

Nondiabetic hyperglycemia means your blood glucose (sugar) level is high even though you do not have diabetes. Hyperglycemia may happen suddenly during a major illness or injury. Or, hyperglycemia may happen over a longer period and be caused by a chronic disease (diabetes type I or II).

What time of day is blood sugar highest? ›

The dawn phenomenon, also called the dawn effect, is the term used to describe an abnormal early-morning increase in blood sugar (glucose) — usually between 2 a.m. and 8 a.m. — in people with diabetes.

Which finger is best for glucose testing? ›

Recommended finger: the World Health Organisation recommends the middle or ring fingers are used for blood glucose tests (second and third fingers). You may want to avoid using your little finger due to the skin being thin.

How does squeezing finger affect blood sugar? ›

On average, blood sugar readings were lower when people put pressure on the finger. The finding, according to the researchers, is in line with advice to avoid firm squeezing of the tested finger.

Can I brush my teeth before a fasting blood test? ›

Yes, brushing your teeth is permitted unless otherwise indicated by your physician, assuming you do not use large amounts of toothpaste and swallow the lather.

What are the warning signs of prediabetes? ›

Symptoms
  • Increased thirst.
  • Frequent urination.
  • Increased hunger.
  • Fatigue.
  • Blurred vision.
  • Numbness or tingling in the feet or hands.
  • Frequent infections.
  • Slow-healing sores.
17 Mar 2022

How long should you avoid sugar before glucose test? ›

The first is done fasting (after you have had nothing to eat or drink for at least 8-12 hours prior—except water). Then you will be given a glucose liquid to drink that has a specific amount of sugar in it. Blood samples will be taken one, two, and three hours after you have completed this drink.

What happens if you don't wipe the first drop of blood? ›

Discarding the first drop of blood and refraining from squeezing the finger makes measurements more complex and necessitates deeper and more painful punctures.

Why is it not advisable to squeeze the finger after pricking? ›

Wipe away the first drop of blood because it may be contaminated with tissue fluid or debris (sloughing skin). Avoid squeezing the finger or heel too tightly because this dilutes the specimen with tissue fluid (plasma) and increases the probability of haemolysis (60).

Why do I get different blood sugar readings on different fingers? ›

Contamination of the fingers is a common culprit in blood sugar reading variability. That's because it only takes a little bit of food residue on your hands to impact blood glucose levels.

Videos

1. HbA1c vs Fasting Blood Sugar | Difference Between HbA1c and Fasting Blood Sugar Test
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2. What is a Normal Blood Glucose Level?
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3. What Is The Difference Between Fasting Plasma Glucose Test And An Oral Glucose Tolerance Test?
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4. Fasting Blood Glucose | Random Blood Glucose | OGTT | HbA1C | Laboratory Tests | Dr Asif Lectures
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5. What is Normal Fasting Blood Sugar Levels on Intermittent Fasting? – Dr.Berg
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6. How to test your blood glucose (sugar) levels
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