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What Is Fasting Blood Sugar Test

How Long Should I Fast Before Blood Test

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

You are required to fast for up to 12 hours before going for a blood test. Drinking coffee, tea or even water can affect blood test results.

Avoid Over Fasting, this particularly applies to diabetic individuals and pregnant women. Over fasting can cause dehydration and hypoglycemia in diabetics. Over fasting can also sometimes alter test results.

Make sure to carry some snacks to your physicians office so that you can eat immediately after blood is drawn. Blood glucose for postprandial levels requires you to eat and give a blood sample after an hour of a meal.

Hopefully, this article has given you a good idea about fasting for blood tests and which blood tests require fasting. These questions should additionally be clarified with your physician. This is because your physician will be able to guide you better.

Medically Reviewed By

Dr. Himanshi is a Homoeopathic consultant and currently working as a lecturer in Post-graduate faculty of Homeopathy, Parul University, Vadodara. Completed BHMS and MD in Homeopathy in January 2018 and also has a clinical experience of about 6 years. Personal interests include reading, spending time with family and traveling.

Diabetes And The Hemoglobin A1c Test

The hemoglobin A1c test , is an important diabetes blood test used to determine how well your diabetes is being controlled. This diabetes test provides an average of your blood sugar control over a six- to 12-week period and is used in conjunction with home blood sugar monitoring to make adjustments in your diabetes medicines. The HbA1c level can also be used to diagnose diabetes if a value of equal to or greater than 6.5% is found.

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.

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Can We Drink Water Before Fasting Blood Sugar Test

Can we drink water before fasting blood sugar test? If youre asked to fast, you cant eat anything for 8 to 10 hours before the test. You should drink only water. If you are having an OGTT, you will need to adjust your diet for a few days before the test and fast for 8 hours just before the test.

Does drinking water affect blood sugar test?;Its fine to drink water before a blood test, unless youre instructed otherwise by your doctor.

Can you drink water while fasting for blood tests?;Why do I need to fast before my 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 happens if you drink water before a fasting blood test?;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 hadnt had anything.

What To Do If You Broke Your Fast

Fasting Blood Glucose Testing Stock Photo

If you break your fast, the results of your test may be inaccurate. You can call your doctor to see if the test can still be done.

Some tests may be still be analyzed knowing that youre not in a fasted state. Its important to be honest with the test administrator so they can interpret your results properly. Some types of tests may need to be rescheduled.

There are many conditions a doctor might want to test for using a fasting blood test. Just three of many examples include diabetes, high cholesterol, or low iron.

The following early symptoms may indicate you have one of these conditions:

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Also Check: What Is A Normal A1c For A Non Diabetic

Who Should Undergo Fasting Blood Sugar Level Tests

People falling in one or more of the below categories are advised to undergo Fasting Blood Sugar tests: People who have a body mass index higher than 25, regardless of age and who have additional risk factors including high blood pressure, abnormal level of cholesterol, a sedentary lifestyle, a history of Polycystic Ovarian Syndrome, heart disease or any signs of diabetes in the family. People aged 45 or above should get a fasting blood sugar screening done on a regular basis.Women who suffered from gestational diabetes should get tested at least every three years. People diagnosed with pre-diabetes should get tested on an annual basis.

Hba1c Test For Diabetes Diagnosis

An HbA1c test does not directly measure the level of blood glucose, however, the result of the test is influenced by how high or low your blood glucose levels have tended to be over a period of 2 to 3 months.

Indications of diabetes or prediabetes are given under the following conditions:

  • Normal: Below 42 mmol/mol
  • Prediabetes: 42 to 47 mmol/mol
  • Diabetes: 48 mmol/mol

There are two types of blood sugar levels that may be measured. The first is the blood glucose level we get from doing finger prick blood glucose tests. These give us a reading of how high our levels are at that very point in time.

The second is the HbA1c reading, which gives a good idea of our average control over a period of 2 to 3 months. The target blood glucose levels vary a little bit depending on your type of diabetes and between adults and children.

Where possible, try to achieve levels of between 4 and 7 mmol/L before meals and under 8.5 mmol/L after meals. The target level for HbA1c is under 48 mmol/mol .

Research has shown that high blood glucose levels over time can lead to organ and circulation damage.

Keeping blood glucose above 4 mmol/l for people on insulin or certain medications for type 2 diabetes is important to prevent hypos occurring, which can be dangerous.

Your doctor may give you different targets. Children, older people and those at particular risk of hypoglycemia may be given wider targets.

FREE blood glucose level chart

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Why Is A Fasting Blood Test Important

Food, most drinks, and strenuous exercise can all lead to inaccurate blood test results. If the results of the blood test are unclear, the process will have to be completed again to get numbers that reflect your true state of health.

In most cases, water may be consumed before a fasting blood test. If youre currently taking any medications, check with your doctor to see if you can take your regular dosage without affecting the results.

Fasting actually affects the results of very few blood tests.

For example, measurements of kidney, liver, and thyroid function, as well as blood counts, are not influenced by fasting.

Fasting is required before commonly ordered tests for:

  • glucose
  • triglycerides
  • anaemia for accurate results.

What Is Being Tested

What is fasting blood sugar?

Glucose is the primary energy source for the bodys cells and the only short-term energy source for the brain and nervous system. A steady supply must be available for use, and a relatively constant level of glucose must be maintained in the blood. Glucose tests measure the level of glucose in your blood or detect glucose in your urine.

A few different protocols may be used to evaluate glucose

Glucose is the primary energy source for the bodys cells and the only short-term energy source for the brain and nervous system. A steady supply must be available for use, and a relatively constant level of glucose must be maintained in the blood. Glucose tests measure the level of glucose in your blood or detect glucose in your urine.

A few different protocols may be used to evaluate glucose levels. This article focuses on:

  • Fasting blood glucose this test measures the level after a fast of at least 8 hours.
  • Random blood glucosesometimes your blood glucose will be measured when you have not fasted .

Other types of glucose tests include:

  • A glucose tolerance test measures glucose levels after fasting and after you drink liquid containing a specific amount of glucose .
  • A specific protocol is used to help diagnose gestational diabetes, which is diabetes that first develops during pregnancy .
  • Urine is routinely tested for glucose as part of a urinalysis.

Diabetes is the most common disease resulting from an imbalance between glucose and insulin.

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A Need To Update Older Guidelines

Aldasouqi also points out that specialists currently recognize that eating before undergoing a blood cholesterol test is unlikely to affect relevant measurements. Therefore, having a meal before going in for a test may actually be better than fasting and potentially losing consciousness on the way to the laboratory.

He adds that the idea of fasting before a blood test comes from antiquated sets of guidelines from the 1970s, which specialists in Canada and most European countries no longer use.

For this reason, he says that United States-based specialists may want to consider revising their own guidelines to better fit the needs of their patients.

According to the studys findings, only 35 percent of participants had received advice about how to prevent a FEEHD event before going in for a blood cholesterol test.

We encourage patients who receive orders for a lab test, explains Aldasouqi, to ask their doctor if fasting is really necessary, and if so, how they should handle their diabetes medications during the fasting period to account for the changes in their blood sugar levels.

FEEHD is overlooked in clinical practice, and we aim to bring this problem to light and further educate doctors and patients about the consequences of fasting while on diabetes medications, he adds.

What Do The Results Of The Blood Glucose Test Mean

Normal fasting blood glucose — or blood sugar — is between 70 and 100 milligrams per deciliter or mg/dL for people who do not have diabetes. The standard diagnosis of diabetes is made when two separate blood tests show that your fasting blood glucose level is greater than or equal to 126 mg/dL.

However, if you have normal fasting blood sugar, but you have risk factors for diabetes or symptoms of diabetes, your doctor may decide to do a glucose tolerance test to be sure that you do not have diabetes.

Some people have a normal fasting blood sugar reading, but their blood sugar rapidly rises as they eat. These people may have impaired glucose tolerance. If their blood sugar levels are high enough, they may be diagnosed with diabetes.

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Blood Sugar Testing At Home

A person can test their blood sugar levels at home.

In most cases, doctors ask people to measure fasting blood sugar immediately upon waking and before they have anything to eat or drink. It may also be appropriate to test blood sugar before eating or sometimes 2 hours after a meal when blood sugar has returned to normal levels.

The right time to test is dependant on treatment goals and other factors. For example, most people with diabetes do not need to test between meals unless they are using a diabetes drug that can lower blood sugar. Other people may test between meals if they feel their sugar levels may be low.

Since they do not make any insulin, some people with type 1 diabetes need to test several times a day. They do this because they need to check their levels regularly in order to adjust their insulin dose at that time.

To do the blood sugar test, a person will:

  • Prepare the testing strip and glucose monitor to be ready for the blood sample.
  • Clean the testing area, usually the side of a fingertip, using an alcohol swab.
  • Lance the testing area. Bracing against a firm surface can help with the impulse to pull away.
  • Squeeze the testing area around the wound to maximize blood flow.
  • Squeeze a drop of blood onto the test strip.
  • Put the strip into the monitor.
  • Record the time, blood sugar reading, and recent food intake in a log.

Blood glucose monitoring kits for use at home are available for purchase online.

Can You Drink Coffee If Youre Fasting Before A Blood Test


Even if you drink it black, coffee can interfere with blood test results. Thats 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. The less hydrated you are, the harder it can be for the nurse or other medical professional whos doing your blood test to find a vein. This can make the blood test harder or more stressful for you.

Read Also: How Much Vitamin B12 Should A Diabetic Take

What Is The Fasting Blood Sugar Test Used For

The fasting blood sugar test is also used to test the effectiveness of different medication or dietary changes on people already diagnosed as diabetic

Fasting blood sugar levels are measured by taking a blood test after a period of fasting, usually of 8 hours without food. Typically, fasting blood glucose levels are taken in the morning before any breakfast is eaten. When having your fasting blood glucose levels take, you should not have any drinks apart from water during the period of fasting.

A fasting blood glucose test can be useful to see how well the body is able to manage blood sugar levels in the absence of food. When we do not eat for several hours, the body will release glucose into the blood via the liver and, following this, the bodys insulin should help to stabilise blood glucose levels.

A fasting blood glucose test therefore shows:

  • Whether the body is able to bring down the raise in blood glucose levels from the previous meal
  • How effectively the body copes with its own release of glucose

The target for fasting blood glucose levels are the same as the targets for before meal readings.

  • For adults with diabetes, the target level is between 4 and 7 mmol/l
  • For children with diabetes, the target level is between 4 and 8 mmol/l

However, ;some people may be set individual targets, by their doctor, that differ to the above levels.

How Is The Test Done

Your healthcare provider may poke your finger with a small needle and fill a small tube with the blood. Or a small amount of blood may be taken from your arm with a needle. The blood is sent to a lab.

Having this test will take just a few minutes.

Ask your healthcare provider when and how you will get the result of the test.

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What To Know About Fasting Before Your Lab Test

With certain blood tests, you may be instructed to fast for up to eight hours before your appointment. Fasting before a blood draw means you dont eat or drink anything except water. Dont wait until the day of your blood draw to ask if you should fast. That could cause your appointment to be rescheduled. If at any point youre unsure if fasting is required, contact your doctor.

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Other Blood Tests That Require Fasting

What Should Your Fasting Blood Sugar Levels Be?

People may be asked to fast for:

  • Basic or comprehensive metabolic tests: Tests for blood sugar, electrolyte balance, and kidney function. Typically, people will be asked to fast for 10 to 12 hours before having one of these tests.
  • Renal function panel: Tests to see how well the kidneys are working. Typically, people are asked to fast for 8 to 12 hours before these tests.
  • Vitamin B12 test: Tests for the levels of the vitamin B12 in a persons blood. Typically, people are asked to fast for 6 to 8 hours for these tests. They must also let the doctor know what medications they take, as some can interfere with the test.
  • sugar

Measuring the levels of these substances is crucial to diagnose certain conditions, such as:

  • diabetes
  • high cholesterol
  • liver disease

For correct diagnosis of these conditions, it is important that a person fasts. Eating or drinking before the test may raise the levels of a particular substance in the blood, leading to inaccurate results. Incorrect results could lead to a wrong diagnosis.

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What Does The Test Result Mean

Your blood sugar level may be higher than normal if:

  • You have prediabetes .
  • You have diabetes.
  • If you already have diabetes
  • You have not been taking your medicine correctly.
  • Your medicine is not controlling your diabetes.
  • You have not been following your meal or exercise plan.
  • You have kidney or liver disease.
  • Your pancreas is inflamed. The pancreas is an organ in your upper belly that makes insulin.
  • Your body is severely stressed from an illness, infection, surgery, or injury.
  • You are taking medicines, such as antibiotics, steroids, blood pressure medicine or asthma medicine, which can raise your blood sugar.
  • Your blood sugar level may be lower than normal if:

    • You have diabetes and:
    • The dose of insulin or other medicine used to control your diabetes is too high.
    • You took your medicine for diabetes but then did not eat or you exercised too much.
  • Your thyroid, pituitary, or adrenal glands are not working normally. These glands make hormones, which are chemicals that help with things such as growth, development, and control of blood pressure and blood sugar.
  • You have liver disease.

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