What are the rumors about blood donation?

During the Chinese New Year, Beijing's blood supply was tight. There are many patients who need blood, and the blood supply in blood stations is insufficient, and the demand is far greater than the supply, which is very worrying.

Related news (source: people.com.cn)

There are many reasons for the shortage of blood sources, one of which is the insufficient rate of unpaid blood donation; When it comes to blood donation, many readers may think, "Will blood donation lead to obesity? Can high myopia donate blood? "

Let's talk about this today.

The so-called blood donation is to temporarily store the blood of healthy people for patients who need blood transfusion.

The total blood of a normal person is equivalent to 7% to 8% of the body weight, and a person weighing 60 kg has about 4.24.8L of blood. Most of this blood surges and circulates in the cardiovascular system, which is called circulating blood volume; A few stay in liver, lung, abdominal vein, subcutaneous vein, etc. In case of emergency, such as massive bleeding, the circulating blood should be replenished quickly. 1 However, "just in case" is limited. If the patient loses 20% ~ 25% of blood in a short time, or has blood diseases such as leukemia, it will induce blood problems and must be transfused.

Blood components (source: biodiscover.com)

So, what is blood transfusion?

It is a blood component, namely plasma and blood cells.

The main component of plasma is water, followed by gas, electrolyte and small molecule organic matter, and it also contains a certain amount of protein. This makes plasma and interstitial fluid not only related (the contents of water, gas, electrolyte and small molecular organic matter are basically the same), but also different (the interstitial fluid contains little protein). The relationship between the two is roughly equivalent to the relationship between rivers and groundwater. When the river rises, it will go underground and become groundwater. When the water level of the river drops, groundwater will flood into the river to supplement the shortage of the river; Plasma protein mediates and maintains blood osmotic pressure, and indirectly regulates blood volume.

Mutual supplement of river water and groundwater (source: tp.edu)

Blood cells are constantly circulating, but the circulation of blood cells is not flowing, but "reconstruction, destruction and reconstruction". White blood cells, red blood cells and platelets all have a certain life span. Taking white blood cells as an example, there are many kinds of white blood cells, among which neutrophils are the "Depth Charge" to deal with infection. Bone marrow produces neutrophils all the time, but only a small amount of these neutrophils will enter the blood; After entering the blood, stay in the blood for about 8 hours, that is, enter the cell tissue. If there is no infection, these neutrophils will age and die after 45 days, and the newly released neutrophils from bone marrow will fill their own gaps. 1

This is the physiological basis of blood donation. The dosage of blood donation (200ml, 400ml) is very low, far from reaching the warning line of 20% to 25%. Healthy people are fully capable of recovering in a short time.

Having said that, we can analyze the remarks about voluntary blood donation.

Speech 1: Blood donation will affect immunity.

Wrong.

The immune system of human body mainly includes three parts: the barrier composed of skin and mucosa, the innate defense system composed of phagocytes, and the acquired immune system composed of B cells and T cells. Phagocytosis, B cells and T cells belong to leukocytes. As mentioned above, white blood cells have a certain life span, and at that point, the human body will destroy them; At the same time, hematopoietic tissues such as bone marrow have been producing new white blood cells.

Therefore, blood donation will not affect immunity.

Speech 2: Blood donation can lead to fainting.

That's right.

Blood donation may indeed cause fainting, which is often referred to as blood donation reaction. In addition to fainting, blood donation reaction can also cause nausea, vomiting, pallor, palpitation, cold sweat, chest tightness and other symptoms. But overall, the incidence of blood donation reaction is very low, which can be prevented and the consequences are slight.

According to the blood station survey of Weifang Red Cross Center, among more than 40,000 blood donations, only 1 10,000 cases showed blood donation reaction, accounting for about 2.5% of the total. Most of these blood donation reactions occur in first-time blood donors, and the blood donation reactions of soldiers and medical workers are far lower than those of other occupations. This shows that mental factors play a decisive role in blood donation reaction. In addition, hunger, fatigue or hot weather can also affect the occurrence of blood donation reaction. Whatever the reason, these patients returned to normal within minutes after receiving treatment. three

Speech 3: High myopia cannot donate blood.

Controversial.

First of all, referring to the blood donation standards in the United States, Hong Kong and other places, there is no stipulation that high myopia cannot donate blood. 4,5

Secondly, the old version of "Health Examination Standard for Blood Donors" implemented by China 1998+00 in June did point out that "patients with ophthalmic diseases, such as keratitis, optic neuritis, high myopia with fundus changes, etc." Can't donate blood. However, in the 20 1 1 version, that is, the latest version of the Standard for Health Examination of Blood Donors, these words have been modified and deleted, and only "those whose recovery time from active or progressive ophthalmic diseases is insufficient 1 week and those whose recovery time from ophthalmic surgery is less than 3 months" are listed as the objects that cannot donate blood for the time being.

The main difference between patients with high myopia (more than 600 degrees) and ordinary myopia lies in the anterior and posterior diameter of the eyeball. Ordinary myopia usually (pay attention to these two words) only involves refractive system abnormalities, while patients with high myopia usually (pay attention to these two words) obviously lengthen the anterior and posterior diameter of the eyeball.

Eyeball physiology, from left to right, normal, myopia, high myopia (image source: boletinaldia.sld.cu)

The length of the anterior and posterior diameter of the eyeball will lead to many consequences, such as fundus changes. Some studies have pointed out that the fundus blood flow of patients with high myopia will decrease, and further examination shows that the fundus blood vessels of patients with high myopia become thinner. Because human blood vessels are interconnected, slight blood pressure changes after blood donation may affect the fundus blood vessels, causing vasospasm of the fundus blood vessels and the risk of retinal detachment.

High myopia can be accompanied by fundus changes, a: cardiovascular formation; B: macular degeneration; C: macular degeneration and staphyloma; D: grape swelling and shrinking (source: pointsdevue.com)

Therefore, it is not high myopia that affects blood donation, but changes in the fundus. This is also the significance of the new version of the health examination standard for blood donors. Although high myopia is likely to be accompanied by fundus changes, it is not the only reason for fundus abnormalities. If possible, it is best to have a fundus examination before donating blood; If there are no conditions, and it happens to be a high myopia, then, to be on the safe side, you can not give it.

Speech 4: Repeated blood donation will lead to obesity, high blood pressure and other problems.

Wrong.

Since the human body can recover quickly after a single blood donation, and the Red Cross, the government and other blood donation management agencies have made strict regulations on the interval of blood donation, leaving enough recovery period for volunteers, then in theory, multiple blood donations will not have adverse effects on the human body.

Blood donation interval (source: requirements for health examination of blood donors (20 1 1))

In fact, there is no evidence that repeated blood donation will affect health. On the contrary, some studies have pointed out that regular blood donation can improve the blood sugar and blood lipid levels of volunteers. However, there are relatively few samples used in the study, which means that it is unrealistic to improve health through regular blood donation.

Speech 5: You need an empty stomach before donating blood.

Wrong.

Because going to the hospital for a blood test requires an empty stomach, many people think it is necessary to fast before donating blood. This is not right. On the one hand, fasting blood donation is more prone to blood donation reaction; On the other hand, blood tests show blood sugar and blood lipid levels. Blood sugar and blood lipids in the human body are not static, but constantly fluctuating. Long-term fasting will lead to low blood sugar and blood lipid, which will rise again after eating, and then gradually return to normal level under the regulation of the human body. Therefore, in order to measure accurately, we should avoid eating for 8~ 14 hours before checking blood sugar and blood lipid.

Blood donation is not like this. Volunteers donate blood to provide blood for patients. Even if volunteers donate blood after eating, slightly higher blood sugar and blood lipid will be diluted by the patient's original blood; Even if the amount of blood transfusion is large, as long as the patient's regulatory system is normal, blood sugar and blood lipid levels will still return to normal.

So you don't need an empty stomach to donate blood.

refer to

Zhu Danian. Physiology [M]. People Health, 2008.

Li Yulin. Pathology [M]. People's Health Publishing House, 2008.

3 Jiang Shuhua, Wang Lijuan, Ma Xueqin, et al. 1003 cases of blood donation reaction: causes and preventive measures [J]. China Journal of Blood Transfusion, 200 1, 14 (1): 4748.

4 qualification criteria: in alphabetical order [EB/OL]. American red cross, [20 18-02-26]. . The signed articles published on this website only represent the author's views and have nothing to do with this website. If there is any infringement, you are responsible.

Author: Zhao Yanchang