What is the reason for black blood when drawing blood?

When doing blood tests, if you find that the blood is black, don't worry. Generally speaking, this is a normal physiological phenomenon. It is mainly caused by different blood vessels. Human blood contains a certain amount of melanin. When the blood viscosity increases, the melanin will appear denser, causing the drawn blood to appear black.

What should I pay attention to when drawing blood for a physical examination?

1. Get enough sleep

Be sure to go to bed early the night before having your blood drawn, don't stay up late, and get enough sleep to ensure normal detoxification of the liver. If you don't sleep well, the liver function results when you draw blood the next day will often be abnormal, which is not conducive to the diagnosis and treatment of the disease.

2. Make sure to fast on the morning of the blood draw and drink appropriate amounts of water. Because common blood draws such as glucose and blood lipid tests require patients to draw blood while fasting, eating will affect the accuracy of the results.

3. Relax. Some friends have been afraid of injections and blood draws since childhood. They are afraid to even go into the hospital laboratory, or they fail to do so many times. This nervous mood can actually affect the physiological state. Not only will it increase blood pressure, it can also easily secrete hormones that affect the measurement of certain items.

4. Pay attention to exercise. Many friends found out after having blood drawn that their blood vessels were very thin and blood was difficult to draw. It might even take several times to draw blood, which was not only uncomfortable for them but also detrimental to the accuracy of the test results. Therefore, it is recommended that everyone should pay attention to physical exercise and improve physical fitness on weekdays.

5. Can I take a shower? Generally speaking, you can take a shower after having your blood drawn. However, if your blood vessels are punctured and a hematoma occurs, it is recommended that you ask your doctor if you can take a shower. If it is not necessary, you can choose to take a shower the next day.

6. Reasonable diet . Finally, you should keep a light diet three days before blood drawing and avoid consuming too much fat to prevent high blood lipids. If the amount of blood drawn is large, you can pay attention to supplementing some high-protein diet and eat more fresh fruits and vegetables.