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Fasting Rules for Blood Test

Fasting Rules for Blood Test

When undergoing a blood test, fasting rules should be followed diligently. This article will cover some of the rules that are required to be followed that will help you prepare for a blood test.
Batul Nafisa Baxamusa
Last Updated: Apr 24, 2018
There are many medical conditions for which one needs to undergo a blood test. Fasting is advised by doctors, wherein one needs to remain without eating food for a certain period of time. The minute one is told to give their blood for further tests, everything draws a blank in the mind. A needle pricking through the arm used to draw out blood tends to become a chilling site for many patients. Thus, one tends to mix up the rules for fasting before a blood test. There is a lot of confusion about what should be and what should not be done before a blood test.

The Need to Fast
There are many reasons for carrying out a blood test. The health care professional will advice you to fast for a certain time frame. The foods we eat may affect our blood sugar levels as well as lipid level. The test for low density lipoprotein (LDL), high density lipoprotein (HDL), and triglycerides may change drastically after eating. Even in our daily lives, blood and lipid levels in our body change every hour as and when eat. The rate of digestion of certain foods and drinks too affects the blood sugar and lipid levels. In order to minimize any minor or drastic changes in the basic sugar and lipid values in a blood test, one is advised a short fast.

Fasting in case of diabetes helps the doctor understand if a patient is truly diabetic. For example, if the blood test results are greater than 125 mg/dl, it would indicate diabetes. However, if you eat a snack bar before your test, your blood sugar level may rise above 125 mg/dl. The same is the case for fasting for blood work related to lipids. It is seen that the normal LDL, HDL, and triglycerides values are 20 points higher when one is not in a fasting state. Therefore, one could be falsely diagnosed with elevated cholesterol levels even though the lipids are within normal range. To get a correct diagnosis, one needs to follow all the fasting rules for a blood test. If you even have a bite of your favorite snack, you are causing the sugar and lipid levels to elevate and give a false picture regarding the state of your health.

Specific Rules
Our blood flows throughout our body and the blood vessels are full of cholesterol deposits. The blood sugar level too keeps fluctuating all through the day. In this case, one needs to fast so that the sugar and lipid levels come down to their actual range. This will give a correct reading and help the doctor diagnose a condition properly.

Requirements for Triglycerides Levels
It is seen that after eating, the triglyceride levels in our body can rise by 15 to 20% more than normal. Therefore, a 12-hour fast is required in such a case. In some cases, the patient may even be asked to fast for 14 hours, depending on the rate of triglyceride cells reaching the normal level.

Requirements for Cholesterol
The time frame for fasting for cholesterol depends on each case that is decided by the physician. The fasting period may range from 6 to 12 hours, depending on the blood test. One may also be advised to avoid high cholesterol foods a week before taking the blood test. This helps in flushing out the extra cholesterol and brings it down to its actual level. However, one should not undergo a drastic diet change as the body will start using the available cholesterol. This will again lead to an incorrect result due to a natural rise in the cholesterol levels.

Requirements for Blood Sugar
A blood sugar test or blood glucose test is carried out in a similar way as a cholesterol test. One may be asked to maintain a-12 hour fast and give the blood for testing in the night. Therefore, it is always better to avoid eating anything in the night and early morning. The body will thus, not produce any glucose from the starch present in the food, and show normal sugar levels.

General Rules
There are certain general fasting rules related to blood tests that one should follow, for both, blood sugar or cholesterol tests.
  • One should not eat anything, even a tiny bite for the entire fasting period advised by the physician, till the blood is drawn.
  • Avoid smoking, alcohol, chewing gum, etc., during the fasting period.
  • If you are on prior medications, vitamins, herbal supplements, etc., speak to your doctor about it. Some medications, vitamins, herbs, etc., may affect your blood test results. The doctor will be able to advice you whether or not you can continue or stop the medications till the blood is drawn.
  • Do not drink any liquid like tea, coffee, alcohol, juices, and energy drinks during the fasting period. You can only drink plain water to avoid dehydration when thirsty. Do not add lemon or other flavorings to the water.

These are the important rules for fasting before a blood test. If you feel weak and have a little snack during the fasting period, do not hide it. Make sure you tell the lab technician or doctor about it. They might be able to advice you if you can still go ahead with the test or plan the test some other day. After all, you want the right results to show up in your test, don't you?