Why do I need to be on an empty stomach for blood draw? Does drinking water count as being on an empty stomach? I finally figured it out today.

For hospitalization, blood draws are usually done the next morning, except for emergency tests. The nurse will tell you at night that blood will be drawn the next morning, and you should not eat after 12:00 p.m.

We do whatever the doctor says. Although we don't say it, it doesn't mean we understand why we need to fast. In fact, it depends on the examination items. Some examination items do not require fasting.

Two reasons for fasting before blood draw Today we will popularize the reasons for fasting blood test. Why do some tests require fasting before blood draw?

Fasting blood sampling refers to the sample taken on an empty stomach after fasting for 8 hours, usually in the morning before breakfast.

This can avoid the influence of dietary ingredients and daytime physiological activities on the test results. At the same time, since blood is collected at a fixed time each time, it is also convenient for comparison. It seems that fasting for a long time will also affect the accuracy of the test. Even if you have not eaten for 8 hours during the day, you are naturally not fasting.

01

Reference ranges are based on fasting.

All test items in the laboratory have a reference range, and the determination of whether the result is abnormal is based on the comparison of the individual result with the reference range. If it exceeds the reference range, it is considered abnormal. In most cases, the reference range is based on the test results of fasting blood draws from healthy people, and is calculated through scientific statistical analysis.

If a person is not fasting when blood is drawn, there will be a lack of comparability with the reference range, affecting the interpretation of the results.

02

Within half an hour after a person eats, the blood will become chyle.

The testing of many test items requires a colorimetric process. Chyle blood will seriously interfere with the test results. Therefore, when the laboratory encounters chyle blood, it will basically reject the sample and require re-blood sampling!

After looking at this picture, do you still want to eat an egg before having blood drawn?

There are many questions on the Internet, about whether you can drink water on an empty stomach?

Experts say that there is nothing wrong with drinking some boiled water early in the morning on the day of the physical examination, but do not drink beverages, tea, coffee, etc.

In fact, the purpose of fasting is to ensure the accuracy of venous blood laboratory test results during physical examinations.

If you drink a lot of water before a physical examination, it will dilute the blood and cause errors in many test values, but this does not mean that you cannot drink any water at all. Experts explain that it is okay to drink 50 to 100 ml of water in the morning when you have a dry mouth. As long as you don't drink hundreds of ml at a time, it will not affect the physical examination results.

Not all blood draws require fasting. Fasting is usually a requirement for tests such as liver function, kidney function, blood sugar, blood lipids, blood biochemistry (various ions), and blood rheology.

If you want to do these tests, don't ignore the advice to draw blood on an empty stomach! Otherwise, the intake of protein, sugar, purine and other substances in the food will have a significant impact on the content of the indicators to be tested within a few hours!

However, for tests like a routine blood test, eating within a few hours or even a day will not change the number of blood cells to be tested, so if all you need to test is a routine blood test, you don't need to fast.

03

Four things to note when drawing blood for testing

1. It is best to have your blood drawn before 10 am

Before blood draw, it is always emphasized that you should fast, but it is best to fast for more than 8 hours. Generally, the best time to draw blood is between 7:30 and 10:00 in the morning. Especially, do not draw blood after 10 in the morning, because it is affected by physiological endocrine hormones in the body. Even if you are fasting, but the time is too late, the blood sugar value will be distorted.

Do not eat too greasy or high-protein food the day before the physical examination, avoid drinking alcohol, and it is best to fast after 8 pm to avoid affecting the fasting blood sugar and other indicators testing the next day.

2. Stop bleeding with three fingers

After blood is drawn, the platelets have not yet coagulated and the needle hole in the blood vessel continues to bleed. Only by pressing with three fingers can the bleeding be stopped.

However, you must not rub when pressing. Gently rubbing the bleeding area will not only fail to stop the bleeding, but will accelerate the bleeding, which will naturally have the opposite effect. The correct method is to only press and not rub.

3. Clothes should not be too tight

Try to wear loose cotton clothes, and avoid clothes with cuffs that are too small or too tight, to avoid the sleeves not being able to be rolled up when blood is drawn or the sleeves being too tight after blood is drawn, which may cause hematoma in the blood vessels in the arm.

After blood is drawn, you should follow the advice of the examining physician and handle the situation scientifically. If local congestion occurs due to improper compression hemostasis methods, the patient should not be too nervous. Reasonable treatment should be taken under the guidance of a doctor. Generally, the bleeding will stop quickly.

4. Press for 3 to 5 minutes

After blood is drawn, the forearm should be straightened. Normally, it takes 3 to 5 minutes to stop bleeding after blood is drawn. It should be longer for the elderly or patients with abnormal platelets. Some people only press for more than a minute after blood is drawn and think that they are fine. This is wrong.

Source: Public Health Sharing Channel