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How Long For Fasting Blood Work

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Can I Eat And Drink Before Having A Blood Test

Fasting Blood Tests: Can You Drink Coffee? Take Meds? A Doctor Explains

It depends on the type of blood test you’re having. The healthcare professional arranging your test will tell you if you need to do anything to prepare for it.

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 beforehand. You may also be told not to smoke before your test.

Why Is Fasting Required Before Blood Tests

Fasting before a blood test helps improve the accuracy and reliability of the test. Accurate test results are a critical component of diagnosing various health conditions and monitoring the effectiveness of treatment plans.

Your diet contains a range of nutrients, including carbohydrates, proteins, fats, minerals and vitamins. When you eat and drink normally, those nutrients are broken down and absorbed into your bloodstream. This can impact the levels of those substances in the blood and skew lab test results.

For example, certain methods of diabetes testing measure the patients baseline blood sugar levels after a period of fasting. Eating directly before the test will cause the patients blood sugar to spike, leading to an inaccurate test result. The patient could be misdiagnosed with prediabetes or diabetes, unless their doctor recommends that they complete a second test.

Sexually Transmitted Infection Tests

Rapid testing is available for HIV tests, often at community health centers and clinics. According to Columbia University, these tests most commonly provide results in 10 to 20 minutes. Doctors also use blood tests to test for the presence of conditions such as herpes, hepatitis, and syphilis. These results may take up to one to two weeks.

Be aware that swabs and urine tests may be the preferred method for some STI testing. Results can also take longer if cultures need to be grown.

Some STIs dont show up immediately after theyre transmitted, so your doctor may order a follow-up test a certain period of time after a negative result.

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What Can I Eat & Drink While Fasting Before A Blood Test

A common question from patients is, Can you drink coffee before a blood test?. The answerunless your doctor specifically tells you otherwiseis no.

Other activities your doctor willlikely have you refrain from include chewing gum, smoking and exercising. Allcan accelerate your digestion, which can adversely affect your results.

Important note: You should continue to take your prescribed medication while fasting unless your doctor specifically directs you not to.

Test Examples With Different Fasting Rules

Fasting Plasma Glucose Test Infographic

Depending on the type of blood test you are having, your doctor will give you specific instructions about fasting for blood tests. Be sure to follow them carefully. In some cases, your doctor will allow you to eat or drink anything before your test. Here are different types of blood tests with different requirements:

  • Fasting Blood Glucose Test: You should not eat or drink anything for at least 8-10 hours before having this test. You can drink water though. The test helps diagnose diabetes.
  • Iron Blood Test: You will have to come to the lab in the morning to take this blood test. You should take this test on an empty stomach. It is important to skip your iron pills stop taking them for 24 hours before the test. These pills can change your test results by raising your iron levels. The test helps diagnose iron deficiency anemia and other similar conditions.
  • Blood Cholesterol Tests : Your doctor may ask to you avoid eat anything for at least 9-12 hours before your test. If your doctor has ordered a lipid profile, it means they want to see levels of different types of cholesterol, including LDL cholesterol, HDL cholesterol, total cholesterol, and triglycerides.
  • Gamma-Glutamyl Transferase Test: Your doctor orders this test to diagnose liver disease. Therefore, you GGT levels will change if you drink alcohol within 24 hours prior to the test. Smoking may also alter test results. It is therefore important you do not drink or smoke before your test.

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Where Should Cholesterol Be Checked

Its best for your primary care doctor to do the test. As noted, your cholesterol levels represent just one of many factors affecting your cardiovascular health. Your primary care physician will have a fuller understanding of your personal and family history, as well as any other risk factors that might apply.

If your cholesterol is checked at a public screening, they may measure your HDL cholesterol and total cholesterol. But if HDL cholesterol isnt measured, knowing your total cholesterol levels still gives you valuable information. Getting your blood cholesterol, blood pressure, body mass index and fasting blood sugar measured regularly should be part of your overall personal care plan.

If you obtain cholesterol screening results from a source outside of your doctors office, be sure to share those with your primary care physician. Additional data points help to establish your cardiovascular risk. This is particularly important for people who smoke, have other health conditions such as diabetes or inflammatory conditions, or have a family history of heart disease, high blood pressure or stroke.

Written by American Heart Association editorial staff and reviewed by science and medicine advisers. See our editorial policies and staff.

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Can Other Blood Glucose Tests Be Used To Diagnose Type 2 Diabetes And Prediabetes

Yes. Health care professionals also use the fasting plasma glucose test and the OGTT to diagnose type 2 diabetes and prediabetes. For these blood glucose tests used to diagnose diabetes, you must fast at least 8 hours before you have your blood drawn. If you have symptoms of diabetes, your doctor may use the random plasma glucose test, which doesnt require fasting. In some cases, health care professionals use the A1C test to help confirm the results of another blood glucose test.

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Preparing For Your Test

Patient Instructions

12 hours is the optimal fasting period. Fasting longer than the recommended time could compromise your results. You may be advised to defer the test to another day.

General Fasting information

To ensure your test is accurate it is important to adhere to the following:

  • Have nothing to eat or drink for at least 10 to 12 hours – preferably an overnight fast
  • If you are thirsty, sips of plain water only are permitted. .
  • You are advised to avoid smoking
  • You are advised not to chew gum
  • If you take medication, please continue to take your medication as prescribed
  • If you are diabetic please consult your doctor prior to fasting
Note:
12 hours is the optimal fasting period, but 10-14 hours is acceptable. Fasting beyond 14 hours affects the quality of the result.

Tips for nervous patients

If blood tests make you nervous, we have special options that will put you at ease.The first step it to let us know how youre feeling. If you have a tendency to become lightheaded when your blood is taken, our staff can have you lie down. This will help you to relax. If you start to feel faint, you can just close your eyes and breathe deeply. Our staff encounter nervous patients all the time are ready to help in any way they can.Practising self-care can also help to ease anxiety.

  • Focus on your breathing
  • Talk about your family, pets, or things you enjoy
  • Try not to hold your breath, tense up or look at the needle.

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Disclaimer

What Should You Not Eat The Day Before A Blood Test

Testosterone as a Fasting Blood Test?

What should you not eat the day before a blood test? Blood glucose tests are either random or fasting tests. For a fasting blood glucose test, you cant eat or drink anything but water for eight hours before your test. You may want to schedule a fasting glucose test first thing in the morning so you dont have to fast during the day.

What should you not eat the night before blood work? 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.

Does what you eat the day before affect blood work? 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. Its recommended that you avoid coffee and other liquids during your fast, McKnight said.

What can you not eat 24 hours before blood work? To ensure accurate results, people are asked not to eat anything on the morning of the test. Some people may take iron supplements or multivitamin tablets that contain iron. These can also affect results. If a person regularly takes these supplements, they should not take them for 24 hours before the iron blood test.

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Type 2 Diabetes Screening By Pharmacists

Some pharmacists offer short appointments where you can find out your risk of developing type 2 diabetes. You usually pay a fee for this service, which involves answering a series of questions.

A diabetes screening test does not diagnose you and is not completely accurate. Instead, it can be used as a guide. Depending on the results from this screening, you or your loved one may be advised to seek further medical help from your local GP. If you dont appear to be at risk at the time of screening, this doesnt mean you arent still at risk of developing type 2 in the future. If you later find signs of diabetes its worth being screened again, or being tested for diabetes.

Some pharmacists offer blood tests to diagnose diabetes, but youll need to pay for these unlike having them through your doctor.

Check your risk

If you dont want to attend a diabetes screening test but want to know your risk of developing type 2 diabetes, you can check your risk for free by using our online risk score.

What If I Accidentally Eat Or Drink Before My Blood Test

If you have been instructed to fast before your blood test and you accidentally eat or drink something during the fasting window, it is important to notify your healthcare provider or the person drawing your blood. If you dont, your results could be incorrectly interpreted.

It may be possible for your healthcare provider to interpret the non-fasted test results. Most likely, they will instruct you to reschedule the blood test at a time when you will be able to successfully complete the fast before the test.

Your physician will let you know the steps you need to take before your blood test, including whether or not fasting is required and for how long. By following all testing instructions and best practices , you can ensure a smooth testing process and the most accurate results.

*Post reviewed and approved by Dr. Sona Kirpekar, our in-house Medical Consultant.

Before you go

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A1c Results And What The Numbers Mean

*Any test used to diagnose diabetes requires confirmation with a second measurement, unless there are clear symptoms of diabetes.

Diagnosis*
Diabetes 6.5 percent or above

When using the A1C test for diagnosis, your doctor will send your blood sample taken from a vein to a lab that uses an NGSP-certified method. The NGSP, formerly called the National Glycohemoglobin Standardization Program, certifies that makers of A1C tests provide results that are consistent and comparable with those used in the Diabetes Control and Complications Trial.

Blood samples analyzed in a doctors office or clinic, known as point-of-care tests, should not be used for diagnosis.

The A1C test should not be used to diagnose type 1 diabetes, gestational diabetes, or cystic fibrosis-related diabetes. The A1C test may give false results in people with certain conditions.

Having prediabetes is a risk factor for developing type 2 diabetes. Within the prediabetes A1C range of 5.7 to 6.4 percent, the higher the A1C, the greater the risk of diabetes.

If I Need A Fasting Blood Test Am I Allowed To Eat Or Drink Anything

Vitamin Blood Test Fasting

Some tests let you have a few sips of water. However, other tests dont even allow water. You should avoid coffee and gum before a fasting lab test because both substances affect your digestive system and can change the results of your test. You should also avoid alcohol, smoking and exercise.

If you take medications, continue taking them as normal unless your doctor says otherwise. If you take vitamin/mineral supplements, ask your doctor whether you should continue to take those.

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Do You Really Have To Fast Before A Blood Test

According to new research and guidelines, for some common tests like the lipid profile assessing cholesterol levels and triglycerides there is no real negative implication if they are performed in a non-fasting state, which actually simplifies the test for the patients.

  • Mosbys Diagnostic and Laboratory Test Reference, 14th EditionKD Pagana Elsevier, 2019
  • Fasting for a blood test.MedlinePlus US National Library of Medicine
  • A Test in Context: Lipid Profile, Fasting Versus Nonfasting.BG Nordestgaard Journal of the American College of Cardiology, Sep 2017
  • Duration of Fasting, Serum Lipids, and Metabolic Profile in Early Childhood.LN Anderson The Journal of Pediatrics, Jan 2017
  • Nonfasting for Routine Lipid Testing. From Evidence to Action.S Mora JAMA Internal Medicine, Jul 2016

Most Frequent Fasting Blood Test Lists:

If your doctor asks for a blood test out of this list, please take the lab advice and your doctor recommendations about medications.

  • Fasting blood glucose test requires 8 to 10 hours fasting period before taking the blood sample, only water is allowed, no eating, snacks, caffeine, fruits, or juices.Glucose tolerance test test requires 6 hours fasting from foods and drinks before the first sample.Glycated hemoglobin test does not need fasting because A1C levels independent on glucose levels which affected by meals or antisugar pills.Why fasting before a sugar test? Because blood glucose level is rapidly increase 30 minutes after meals and rapidly reduced after taking glucose-reducing medications.
  • The Comprehensive Metabolic Panel tests require 10 to 12 hours fasting from foods, drinking, alcohols, smoking, snacks, except drinking water which is not affecting CMP results, CMP blood tests include the following tests:

However, some tests from CMP doesnt require fasting if its requested alone, see non-fasting blood tests list below.

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Why fasting from alcohols is must for GGT test?As alcohols and smoking cause damage to your liver integrity and release GGT enzyme from liver cells into the blood stream, Alcohols are the primarily responsible for the high level of the GGT enzyme in the blood, GGT is an alcohol fasting blood test.

Albumin5 Nucleotidase

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A1c Tests Can Be Affected By Changes In Red Blood Cells Or Hemoglobin

Conditions that change the life span of red blood cells, such as recent blood loss, sickle cell disease, erythropoietin treatment, hemodialysis, or transfusion, can change A1C levels.

A falsely high A1C result can occur in people who are very low in iron for example, those with iron-deficiency anemia. Other causes of false A1C results include kidney failure or liver disease.

If youre of African, Mediterranean, or Southeast Asian descent or have family members with sickle cell anemia or a thalassemia, an A1C test can be unreliable for diagnosing or monitoring diabetes and prediabetes. People in these groups may have a different type of hemoglobin, known as a hemoglobin variant, which can interfere with some A1C tests. Most people with a hemoglobin variant have no symptoms and may not know that they carry this type of hemoglobin. Health care professionals may suspect interferencea falsely high or low resultwhen your A1C and blood glucose test results dont match.

Not all A1C tests are unreliable for people with a hemoglobin variant. People with false results from one type of A1C test may need a different type of A1C test to measure their average blood glucose level. The NGSP provides information for health care professionals about which A1C tests are appropriate to use for specific hemoglobin variants.

It May Not Be Necessary To Fast Before A Routine Cholesterol Check A Large Community

Fasting for a Blood Test | WebMD

This article is a collaboration between MedPage Today and:

It may not be necessary to fast before a routine cholesterol check, a large community-based population study suggested.

Overall, the mean cholesterol subclass levels varied by less than 2% for total cholesterol and high density lipoprotein cholesterol, by less than 10% for calculated low density lipoprotein cholesterol, and by less than 20% for triglycerides, reported Christopher Naugler, MSc, MD, of the University of Calgary in Alberta, and colleagues.

Action Points

  • It may not be necessary to fast before a routine cholesterol check.
  • Note that the researchers found only a few statistically significant differences among cholesterol subclass levels for fasting intervals when compared with either a 9- to 12-hour fasting time or a greater than 8-hour fasting time.

This finding suggests that fasting for routine lipid level determinations is largely unnecessary, they said in the Nov. 12 Archives of Internal Medicine.

The finding is not new and corroborates results from smaller observational studies.

Naugler and colleagues noted that fasting is inconvenient for patients and may discourage compliance with routine screening programs.

They also suggested that eating before cholesterol testing can highlight insulin resistance, which is associated with worse postprandial lipid or lipoprotein clearance. In addition, high triglyceride levels after eating are excellent predictors of insulin resistance.

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