When drawing blood on an empty stomach, what does “empty stomach” mean?

Fasting blood drawing is a common clinical examination method, also known as routine blood test. This examination can help us understand the true condition of the human body.

Our blood collection nurses often encounter such problems

Nurse: XXX, this test requires fasting. Have you eaten?

Patient: I just drank a little milk in the morning and didn't eat anything.

In the patients' minds, they think that eating rice and other foods does not count as fasting, and milk is liquid, so it doesn't matter if you drink it. So if the patient drinks a little milk, does it count as fasting? Let me explain it to you in detail.

What is fasting?

The so-called "fasting" generally refers to not consuming calories, such as not eating staple foods, meat, eggs, milk and other foods, without strictly restricting drinking water. The general fasting requirements for blood tests require fasting for at least 8 hours, preferably 12-14 hours, but not more than 16 hours. This state is clinically called the fasting state. In addition, for a period of time before the blood test, you must maintain a normal diet, eat a light diet, avoid drinking, eating a lot of greasy food, etc., to avoid affecting the test results. In this way, the test results will be more universal and representative, and can represent the levels of some indicators in our daily life, which will help us to clarify the judgment of some diseases in clinical practice.

How to achieve “empty stomach”?

Generally, dinner is eaten between 18:00 and 20:00 the day before blood collection, but no food is eaten after 20:00 (no later than 22:00 at the latest). By 6:00 in the morning on the day of blood collection, you will have been fasting for more than 8 hours. It would be better if you can persist for about 12 hours, so that the body is in a state of low nutrition and low water.

The time for blood collection is also very important. It is best to arrange blood collection between 7:00-9:00 in the morning and no later than 10:30. During this period, the human endocrine system is relatively stable and hunger is tolerable.

If the fasting time is too long, some tests will have abnormal results due to the influence of physiological endocrine hormones in the body. For example, serum bilirubin may increase due to longer fasting time, and blood sugar may decrease and become hypoglycemia due to long fasting time.

What are the “fasting” check items?

Our common ones are:

Ø Fasting blood sugar

Fasting blood sugar is a test item used to diagnose diabetes. You should avoid eating and drinking for at least 8-10 hours before the test. Drinking a small amount of water is allowed (only boiled water, but no more than 200ml, milk, beverages, and tea are not allowed)

Ø Liver function (mainly bilirubin, transaminase)

Ø Renal function (mainly blood uric acid and blood urea)

Ø Blood viscosity (blood rheology)

Ø Blood lipid analysis

At this point, I have to mention that some diabetic patients, because they listened to the doctor's advice to draw blood on an empty stomach, stopped eating anything and even rashly stopped taking the necessary hypoglycemic drugs. This is wrong, because hunger has a particularly obvious impact on diabetic patients. If they are hungry for a long time, they will experience hypoglycemia shock, cold sweats all over their body, and even faint. In the end, they have to be injected or take oral glucose to be out of danger. Stopping the medication rashly will also put themselves at risk of diabetic ketoacidosis.

There are projects that require fasting blood collection, and of course there are projects that do not require fasting blood collection.

Routine blood analysis, coagulation function, erythrocyte sedimentation rate, C-reactive protein, myocardial markers, muscle enzymes, hepatitis B antigen and antibody spectrum, hepatitis C antibody, syphilis and AIDS, five immune items, tumor markers, rheumatology-related autoantibodies, etc.

In addition to the items that require fasting blood drawing and those that do not, we also have more special testing items that require us to draw blood at special times, such as the six items of female hormones. The purpose of the examination is different, and there are specific requirements for the time of blood drawing for the six items of sex hormones. If you want women to understand the function of the ovaries and determine whether the hormones match, you need to draw blood on the 2nd to 4th day of menstruation, so that the results are more accurate.

When we are unsure whether we need to have blood drawn on an empty stomach or not, or when we need to have blood drawn at a special time, it is recommended that we communicate with our prescribing doctor to avoid unnecessary trouble.

Friendly reminder: Things to note when drawing blood:

1. Relax when drawing blood to avoid vasoconstriction due to excessive tension, which will increase the difficulty of blood drawing.

2. You need to wear loose and comfortable clothes on the day of the examination. If the sleeves are too tight after blood collection, it may easily cause vascular hematoma or prolonged bleeding.

3. After the blood is collected, the platelets have not completely coagulated and the needle hole in the blood vessel is still bleeding. You need to gently press the needle hole and the area two centimeters above the needle insertion point with a cotton swab for 3-5 minutes to stop the bleeding. The pressing time needs to be appropriately extended for those who are older or have abnormal platelets. The correct pressing method is as important as superb blood collection technology. If local congestion occurs, you can use a warm towel for wet compress after 24 hours to promote absorption. There is no need to worry too much.

4. After blood collection, you should take a short rest. If you experience symptoms such as dizziness, blurred vision, fatigue, etc., you should lie down immediately and drink a small amount of sugar water. Wait until the symptoms are relieved before proceeding to the next step of examination.

Submitting unit: Chongqing Institute of Population and Family Planning Science and Technology

Audit expert: Yang Lujun

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