In what cases can't blood be drawn for physical examination

Blood tests are the most common method of examination. They may be performed during physical examinations or due to colds. When performing blood tests, you should also be aware of some precautions and taboos. There may be some diseases that you must pay attention to when performing blood tests. In this regard, you must consult a doctor in a timely manner. In addition, after the examination, you should supplement your diet in a timely manner.

Why can't you draw blood for a physical examination?

What are the precautions before having a blood test? Nowadays, some people think that having a blood test will result in blood loss, which is a misunderstanding. In fact, although it seems that several tubes of blood are drawn, each tube only contains 3 to 5 ml. A general physical examination contains less than 20 ml of blood in total. The normal human body has an average of 4,000 ml of blood, and it will regenerate automatically, so don't worry.

What should I pay attention to before taking a blood test?

1. Fasting. It is best not to eat high-protein or greasy foods or drink alcohol the day before blood collection, because these foods and alcohol will directly affect the proportion of blood components, which in turn affects the test results.

2. On an empty stomach. Because the content of substances in a person's blood changes after eating, it is difficult to obtain stable test values ​​after drawing blood on a full stomach. Experts require that the subjects should fast for more than 10 hours from the night before to the next morning. During this time, various chemical substances in the human blood can reach a relatively stable state, ensuring the accuracy of the test results.

3. Relax. If a person is too nervous, it will cause blood vessels to constrict, making blood drawing difficult, so you should keep relaxed when having blood drawn during a physical examination.

4. To avoid bleeding from the needle hole. After drawing blood, you need to press with a medical cotton swab for three to five minutes. Never rub it with your hands, otherwise it will cause subcutaneous hematoma. If there is bleeding after compression, the compression time should be prolonged.

5. If you experience the following symptoms after blood drawing, including dizziness, blurred vision, and weakness, you should lie down immediately and drink a small amount of sugar water. Wait until these symptoms are relieved before continuing the physical examination.