Do I need to fast for blood test?

Most people have some anxiety before coming to the hospital:

Do you want a blood draw?

Do I need to fast?

What is fasting?

........

Today I will take you to understand the above issues

1. What is fasting?

The blood test requires fasting: the night before the blood test, the person who wants to be examined should maintain his usual living habits, maintain a normal diet, eat light meals, do not drink alcohol, coffee, or strong tea, and get a good rest. When you get up the next morning, do not eat breakfast, drink little or no water, do not do morning exercise, and go to the hospital calmly to wait for blood collection.

Tips: Even if you haven't eaten for 8 hours during the day, you are not considered fasting; don't eat too greasy or high-protein food, and avoid drinking a lot of alcohol, as the alcohol content in the blood will directly affect the test results. Fast for at least 8 hours before blood collection, preferably 12-14 hours, and it is not recommended to exceed 16 hours.

2. Can I drink water while fasting?

1. You can drink a small amount of water during fasting

According to the "Guidelines for Venous Blood Specimen Collection" issued by the National Health Commission in 2020, a small amount of water can be drunk during fasting blood collection. However, it does not specify how much a small amount is, so clinicians generally advocate not drinking water before blood collection. However, some doctors believe that 50-100 ml of boiled water can be drunk before blood collection, and generally no more than 100 ml will not have much impact on blood collection. Therefore, some patients with diabetes, hypertension, and heart disease need to take a little boiled water to take medicine, which has little effect on the test. If you must take medicine, you must insist on taking it.

2. Don’t drink too much water

It is generally believed that drinking more than 200 ml of water may affect the blood collection results and make the test results inaccurate, but there is no clear experimental confirmation. Fasting requires at least 8 hours of fasting, but fasting does not mean abstaining from drinking. If you are really thirsty and need to drink water, you don’t have to completely abstain from drinking, but you can only drink boiled water, not sugary drinks, coffee, tea, milk, etc.

3. Why do you need to fast for blood tests?

1. Fasting can put the human body in a basal metabolic state, which can eliminate the influence of factors such as diet.

2. The reference range of some test results is the fasting range value. If you are not fasting, the data will lose its reference significance.

3. For some people, the blood will become milky after eating, which will affect the test results.

4. What are the strict fasting test items?

Blood lipids, blood sugar, liver function, kidney function, glucose tolerance test, blood ions, hepatitis B surface antigen, complement C3, rheumatoid factor, insulin, C-peptide, etc.

5. Why is the blood so dark?

Because when blood is drawn, it is usually venous blood that is drawn. Venous blood has a low oxygen content and is dark red in color, which may mistakenly make people think that the blood has turned black.

6. Why does a bruise appear at the needle hole after drawing blood?

The most common cause of bruising after a blood draw is improper pressure after the blood is drawn.

Tips: After blood is drawn, apply pressure on the needle hole for 3-5 minutes to stop bleeding. If bruises appear locally, do not rub them. Apply hot compresses after 24 hours to promote blood clot absorption.

7. After drawing so much blood, do I need to eat a big meal to make up for it?

A tube of blood requires 2-4 ml. The human body has about 4000 ml, and it will be automatically renewed, so there is no need to worry, just eat normally.

Kind tips:

You should relax when having blood drawn to avoid blood vessel constriction due to fear, which will increase the difficulty of blood collection.