Fasting before Blood Tests

Why You Need Fasting Before Blood Tests – Your Questions Answered

There are quite a few who would balk at getting their blood tested. Only under dire conditions would people voluntarily go for a blood check. Being squeamish about blood could be a reason; however, being afraid of what the results could be is a common deterrent.

Tests, especially blood tests are often done to understand the underlying causes of symptoms you may display when you are sick or check an anomaly that may not be discovered under normal circumstances. This is why these tests are known as Diagnostic Tests, where they help the medical practitioner read and diagnose correctly. Most often doctors would ask for two kinds of blood tests i.e. Fasting Blood Test or  Post Fasting Blood Test.

Why is Fasting Before Blood Tests Important?

Some patients would ask the doctor, “what is the need for fasting before blood tests.” and can we take medication before fasting blood test Yet, it’s an important question that needs an answer. We have a few answers for questions you may have. The first question that would obviously be – Why do I need to fast before a test?

The answer lies in the fact that the nutrients and other components present in the food and drinks are absorbed by the blood, which could affect the factors that are measured in some of the tests. Your blood undergoes changes after eating which affect the levels of glucose in our body along with lipids and iron.

To understand the conditions affecting your blood without any other variables involved is the reason doctors ask you to fast for at least 10-12 hours before taking the blood test. Fasting increases the correctness of your lab results. This means that the results of any blood test will be true without being influenced by what you ate before. A clear test report allows the lab technician and doctor to understand the results clearly.

What Would a Fast Mean?

A fast before a blood test means you don’t eat or drink anything except water for 10-12 hours before the test.

Can you Drink Water When Fasting for a Blood Test?

Yes, you can drink water when fasting for a blood test when you feel thirsty.

Can You Drink Coffee or Tea When Fasting before a Blood Test?

No, other than water you can’t have any other beverages like tea or coffee.

Can You Smoke when Fasting before a Blood Test?

Smoking may alter the test results, which means you cannot smoke while fasting.

Can You Exercise while Fasting before a Blood Test?

No, exercising may also bring changes in your blood that may affect the test results.

Why Can I have Water While Fasting?

We need water to keep our veins hydrated, which makes them easier to find and draw blood from during the test. So one should ideally drink plenty of water before a blood test.

How Many Hours Before Should I Stop Eating?

Most often you need to fast for a minimum of 8 hours for most lab tests. However, you should check with your doctor for instructions with regards to the test including the fast period before the test. It is important that you follow the doctor’s instructions.

Are Medications Allowed During the Fast?

You can take your normal medications as scheduled if the blood test is one you have done before. If you are still unsure, then do check with your physician before taking your medication. There are a few medicines that may affect the test results, which is why it is up to the physician to decide what’s best.

If I Don’t Fast Before a Blood Test?

Fasting improves the accuracy of your blood test for a number of diseases. Not following the instructions of the doctor would mean a false positive report, which could lead to a wrong diagnosis. A number of blood tests are used to diagnose a dire condition such as diabetes, cholesterol, and others. An inaccurate report could lead to further testing or medication for the wrong medical condition. You should inform the lab technician if you have eaten something during the fast so that they can make a note of them and consider it while interpreting the report.

What Blood Tests Require Fasting?

There are a number of blood tests that require fasting. The most common one is Glucose Testing, which checks for levels of sugar in your body. There are others such as the Complete Metabolic Profile, the Normal Metabolic Profile, Renal Function Test, Lipid Profile, Cholesterol Range, as well as Vitamin B12 levels. If you have trouble fasting, then you may want to schedule an early morning appointment for the blood test. You can also snack immediately after the test is done.

When Can I Eat After the Blood Test?

You can drink and eat a snack as soon as your blood test is done. Carrying a snack or something to eat after fasting for blood test would be ideal while getting the test done first thing in the morning will help to reduce the period of fasting before blood tests.

Is it Ok if You Eat Before Other Types of Blood Tests?

Yes, it is perfectly alright to eat before a blood test that does not require fasting.

We have tried answering a few oft-repeated questions, however, if you need to know something more then you should definitely check with your physician for it.

Medically Reviewed By
Dr. Bharti Talreja (MBBS, DPM, FAGE, MIPS)She is a Psychiatrist practising in Indore, India.