What and when a patient eats the night before can have an effect on their medical lab results. Eating late or eating foods high in protein or fat can cause the fasting blood levels to be elevated.

Blood tests are done to check abnormalities in blood. Though these tests look clear-cut and uncomplicated, they’re amazingly easy to tilt. This mostly depends on the type of blood test a person is going to have the next morning. Most of the times a patient can eat and drink normally before the tests, whereas there are cases in which a patient is instructed not to eat or drink before the test, these tests are known as fasting blood tests.

Each blood test is independent, so it is essential to ask the doctor to confirm if you should fast before the test or take any other precaution (many tests require a patient to avoid a certain type of food even 5-7 days before a test is conducted). So fasting may be important because what you eat may change test results. In case the confusion persists; call Healthians representative to know details. If the health care provider has confirmed that a patient should not eat anything before the test, then the instructions should not be ignored.

Guidelines for Fasting Blood Tests

• It is important not to eat anything at least 8 hours prior to the test except water.
• For the Lipid test, fasting should be done for at least 12 hours before the test. Water is allowed though.
• Wondering what to eat the night before a cholesterol test? You should go for something which is low in calories, fat, sugary and oil. As all of these food items can affect the test results.
• During blood test fasting, you should even avoid chewing gum or any type of mouth freshener, as they are full of sugar. These high sugar items can lead to glucose spike, which will ultimately affect your test results.
• Alcohol should be avoided for at least 24 hours before the test as it can cause a drop in the sugar level, can alter the enzyme level & can elevate liver function test results.
• Prescription based medications can be taken unless the doctor advises against it. Certain medications, especially birth control pills can change cholesterol levels, so it is advised to stop taking them for a few days before the test.

How are the results altered?

Some test values get affected following digestion of food. After the food is digested, higher levels of glucose remain in the blood for some time. For example, in the case of fasting blood sugar, our own glycogen (if we have not eaten in a while, sugar from the liver in our body is used) is enough to raise the blood sugar for the fasting test.

Below are examples of few common blood tests and what a patient might need to do to prepare for them, including the fasting period:

Lab Test: Fasting Blood Glucose Test

• Instructions: Patient is advised not to eat or drink anything except water for 8 to 10 hours before a fasting blood glucose test.
• Effect on Lab Results: If you eat sugar before getting your blood sugar tested, you will get an inaccurate reading.

Lab Test: Iron Blood Test

• Instructions: Taking iron pills or tablets for 24 hours before the test should be avoided.
• Effect on Lab Results: Our body absorbs iron very quickly from food or pills, so this can result in raised levels of iron and affect the test results.

Lab Test: Blood Cholesterol Test

• Instructions: Fasting for 9 – 12 before the test is instructed.
• Effect on Lab Results: Eating a large amount of food that is high in cholesterol can raise levels of cholesterol in the report.

Lab Test: Gamma-glutamyl transferase (GGT) Test

• Instructions: Fasting is not required for this test, the patient is instructed to avoid alcohol consumption.
• Effect on Lab Results: Alcohol consumption can alter the enzyme levels.

Lab Test: Test For Stomach Or Bowel

• Instructions: A person is advised to take a liquid diet the day before the test.
• Effect on Lab Results: Lab results are not affected.

Lab Test: Complete Blood Count

• Instructions: Fasting is not required.
• Effect on Lab Results: Lab results are not affected.

Important: Fasting should be for at least 8-12 hours, depending on different tests, but a fasting period more than 14 hours is not recommended as it negatively impacts the results.

Foods to Avoid Night Before Blood Test

There are certain food items that one must avoid before appearing for a blood test. These food items can disrupt the levels of a few yet important parameters such as glucose and cholesterol levels. Here’s a list of items that you must avoid before taking a blood test:

1. Skip Processed Food: Deep fried and highly processed food items can mess with your cholesterol or lipid test. Eating these food items a night before the test can lead to inaccurate readings.
2. Avoid Sugary items: If you are going for a blood sugar or diabetes test, you must avoid high sugar food items, such as chocolates, sweets, soda, and fruit juices. These food items can spike your blood sugar levels, which can alter your test results and make them less reliable.
3. No Alcohol: Before you appear for a blood test, you are advised to stay off alcohol at least 24 hours before your test. As alcohol can affect your liver function and blood test.
4. Limit Your Caffeine Intake: Skip coffee, tea, cold drinks, and energy drinks before a blood test, as they can raise your heart rate or blood pressure.
5. Avoid Iodine-Rich Foods: Planning a thyroid test? Then avoid seafood and iodised salt, as these iodine rich food items can change your thyroid hormone levels, leading to misleading test results.

6. Stop Biotin Supplements: Those who are taking biotin as a supplement for hair and skin should stop taking biotin tablets or powder for at least 48 hours before your blood tests. Biotin can affect your hormones and thyroid levels.

People Also Ask

Q. Does eating bad the day before a blood test affect results?

Ans. Certain tests required 10-12 hours of fasting before the sample is collected such as blood sugar and lipid profile test to ensure accurate reading. If you eat before a test that requires fasting, it can disrupt the levels of sugar and fats in your blood, leading to inaccurate results.

Q. I accidentally ate before a fasting blood test, What should I do?

Ans. In this case, inform your doctor or lab assistant immediately. Depending on the amount and what you ate, your doctor can reschedule the test, if it requires fasting. Eating before a fasting blood test can affect your test results, especially if the test involves measures of glucose, cholesterol, and triglycerides.

Q. What to eat the day before a blood test?

Ans. The day before a blood test, especially a fasting blood test, focus on a light, balanced diet and stay hydrated. Avoid fatty, sugary, and processed foods, and limit or avoid alcohol. If fasting is required, it usually means no food or drinks (except water) for 8-12 hours before the test.

Q. Which blood test requires fasting?

Ans. There are certain blood tests that require fasting to ensure accurate results. These tests include fasting blood sugar (glucose) tests, lipid panels (cholesterol and triglycerides), and some vitamin and hormone tests like Vitamin B12 and certain thyroid function tests.

Q. Will eating sugar the day before a blood test affect results?

Ans. Yes, eating high sugar food the day before a blood test can affect your blood test results. Especially, if it’s a glucose or lipid profile test.

Q. Can I chew gum while under medical fasting for blood work?

Ans. No, avoid chewing gum during medical fasting for blood work. Most chewing gums contain sugar, which can alter your blood test results.

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