Fasting Before A Blood Test
The blood test is one of the most widely used medical tests, as it provides a lot of information about a person’s state of health. So much so that it is considered a routine and basic test for almost any medical action.
Blood tests can be used to analyze different parameters. Often, they are ordered based on the suspected diagnosis, although most often include certain values. For example, blood glucose level or blood cell count.
This test is preferably done first thing in the morning. In addition, it is recommended to go fasting, that is, without having eaten or drunk anything in the last eight hours. In this article we explain why.
What can a blood test do?
A blood test involves drawing blood from the patient and analyzing it in a laboratory. Through this test, many different aspects of the body can be studied to obtain information about the state of global health or a particular organ as a result.
An analysis includes a complete blood count. It is the concentration of each of the types of cells in the blood; that is, red blood cells, white blood cells, and platelets. In addition, it allows you to observe the shape of these cells to see if they are normal.
Similarly, numerous biochemical values can be studied, such as the concentration of glucose in the blood or iron. This group includes cholesterol, triglycerides, thyroid enzymes, urea, and so on.
All these parameters are essential to be able to detect certain pathologies. For example, thyroid enzyme values can reveal thyroid disease. Meanwhile, iron and other related elements help assess anemia.
The blood test can even be used to suspect certain types of tumors. Some of them work by releasing specific substances that can be found in the bloodstream.
Why is fasting important before a blood test?
When planning a blood test, you are asked to come to it having fasted for at least 8 hours. That is, it is recommended not to eat or drink anything (except water) during the night before. This is so because food and drink are absorbed into the blood and can alter certain parameters.
However, this fasting is relative and depends on what is going to be analyzed. For example, if the only thing you want to see is the blood count, you do not need to fast. However, in the case of glucose, it is required to be 8 hours in adults and at least 3 hours in children.
On the other hand, in the case of assessing the thyroid, a 4-hour fast is sufficient. For cholesterol, a fast around 12 hours can even be recommended. Also, another aspect to consider is medications.
Certain medications, like foods, can alter blood values. The normal thing is that the doctor who orders the analysis is aware of this and knows if it is necessary to pause the medication or not.
What else to watch out for?
Healthcare personnel usually make other recommendations so that the blood test goes as well as possible. First of all, in addition to fasting, smoking should be avoided just before the test. It seems that tobacco can also alter blood glucose.
You can drink water, but in a moderate way, to quench your thirst. What is totally contraindicated is to drink alcoholic beverages before the analysis. It is also not recommended to exercise the day before, as certain markers can be confused.
Either way, the ideal is for the doctor to do the individual advice. As we have mentioned before, each patient may or may not need to pause the medication, or they can adapt the fast according to the aspects they wish to study.
