Fasting Before Blood Test - Importance, Types, Do’s and Don’ts
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Fasting Before Blood Test

Fasting Before Blood Test – Importance, Types of Tests, Do’s and Don’ts, FAQs

Has anyone’s physician ever prescribed some blood tests and got to know that he/she has to fast before giving their blood samples? Well, blood tests are one of the most accurate, faster, and most accessible way for diagnosing different kinds of health conditions for everyone irrespective of their age and types of sicknesses.

For different types of blood tests, there are different supervisions as well as requirements. Many people might be suggested by their healthcare provider to fast before a blood test. It means they should not eat or drink anything, except water, for several hours before the blood test begins.

Most of you must have wondered why fasting is necessary for specific examinations and not for others.

Why Is It Important To Fast Before Some Blood Tests?

When an individual consumes food and beverages, they go through the whole system of digestion and absorption. As a result, the state of the organs changes after having a meal. When an individual eats and drinks normally, those foods and beverages are absorbed into their bloodstream that could affect the results of the blood tests. There are certain tests that require getting accurate results so that the doctors can suggest the right treatment for the patient. In that case, it becomes necessary for an individual to stay in fasting for a few hours, depending on the test, before giving their blood sample for examination.This way, the food intake generally won’t affect the organs, and the blood counts, and the result would be more precise.

Types Of Tests That Need Fasting

Not all blood tests demand to fasting in advance. Some of the blood tests that will likely need fasting are as follows:

These tests, as mentioned above, are generally known to be conducted when an individual is fasting. But apart from them, there can be more specific kinds of blood tests for a more advanced diagnostic procedure that may require to stay in fasting. In such cases, clarify with the doctor before getting the tests done. If a doctor has prescribed a new blood test or doesn’t mention whether or not someone should fast or for how long, ask them if fasting is needed. Some tests don’t require fasting but do limit certain foods.

Do’s And Don’ts For Fasting Before Blood Tests


  • Asks the doctor for proper medical advice and actively follow them.
  • Be aware of how long a person has to fast before the test.
  • If an individual is on medication, ask the doctor if you can take those medications and follow their instructions.
  • Try to sip plain water.
  • Avoid food at any cost.
  • If accidentally consumed anything, inform the pathologist or testing centre.


  • Avoid caffeine, chewing gum, smoking, and alcohol prior the blood tests as they can alter the condition of the organs.
  • Do not over fast. The general time limit of fasting before the test is 8-12 hours. More than that can be unhealthy.
  • Avoid exercise before the test. It might drain glucose in the body because of starvation.

General FAQs Regarding Fasting Before Blood Tests

How long should one fast before a blood test?

Usually, an individual needs to fast for 8–12 hours before getting a blood test done or as recommended by the physician. Most tests that require fasting are arranged early in the morning. That way, most of the fasting time will be overnight.

Is it fine to drink water before a blood test?

There is no harm in drinking water before a blood test unless an individual is specifically instructed by the doctor to avoid drinking water or a specific test requires it.Always check and make sure to follow the correct instructions.

Is drinking coffee is okay in the fast before a blood test?

Coffee can interfere with blood test results. This is because it contains caffeine and soluble plant matter to some extent, which might alter the test results. Also, coffee is diuretic, which means it can increase the urination frequency. This can lead to dehydration effects in the body. The less hydrated a person is, the harder it can be for the medical team to find a vein to withdraw blood sample. This can make the blood test more stressful.

What if a child needs to fast before a blood test?

Just like adults, children may also need blood tests that require them to fast before going for a test. Child’s paediatrician will let the parents know how long the child should be restricted from eating and drinking.

Fasting for a blood test during pregnancy?

There are few blood tests mandatory for pregnant women. These are aimed to assess any potential health concerns that a mother or her foetus may experience during pregnancy or after giving birth. Some of these tests may require fasting. The gynaecologist will advise the patient how to be prepared for each test.

Generally, fasting is safe if in pregnancy, if the woman is in good health. For overall comfort, the doctor may advise the patient to drink extra water or to remain indoors, especially in hot and humid weather. Fasting may increase the risk of heartburn in some pregnant women. If anyone experiences any uncomfortable or concerning symptoms prior to the test or blood withdrawn, contact the doctor immediately.

What if anyone eats or drinks mistakenly during the fast?

In that case, inform the healthcare provider before getting the test done. The individual can reschedule the test for another time as advised by the doctor.

When can the individual resume eating and drinking again?

As soon as the test is over, an individual may start to eat and drink normally. However, always check with the pathologist to confirm according to the test.

Is there anything one should know about fasting before a blood test?

Feel free to ask all your queries to the doctor or physician about fasting before blood tests.

Medical Tests and Health Checkups Available At House of Diagnostics (HOD).


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Fasting Before Blood Test - Importance, Types of Tests, Do’s and Don’ts, FAQs
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Fasting Before Blood Test - Importance, Types of Tests, Do’s and Don’ts, FAQs
For different types of blood tests, there are different supervisions as well as requirements. Many people might be suggested by their healthcare provider to fast before a blood test.
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