What are the rumors about blood donation?

During the Chinese New Year, there was a blood shortage in Beijing. There are many patients who need blood, but the blood banks have insufficient blood stocks. The demand far exceeds the supply, which is very worrying.

Related news (picture source: people.com.cn)

There are many reasons for the shortage of blood. One of them is the insufficient rate of voluntary blood donation; and when it comes to voluntary blood donation Well, many readers may be wondering: "Will donating blood cause obesity? Can people with high myopia donate blood?"

Let's talk about this matter today.

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

The total blood volume of a normal person is equivalent to 7% to 8% of the body weight. A person weighing 60 kg has approximately 4.24.8L of blood. Most of this blood rushes and circulates in the cardiovascular system, which is called circulating blood volume; a small part is retained in the liver, lungs, celiac veins, subcutaneous veins and other parts to prepare for emergencies and quickly replenish circulation in critical situations such as major bleeding. Blood volume. 1 However, there is a limit to “just in case”. If the patient loses 20% to 25% of his blood in a short period of time,2 or has blood diseases such as leukemia, blood problems will occur and blood transfusions will be necessary.

Blood composition (image source: biodiscover.com)

So, what does blood transfusion deliver?

It is the components of blood, namely plasma and blood cells.

The main component of plasma is water, followed by gases, electrolytes and small organic molecules. In addition, it also contains a certain amount of protein. This makes plasma and interstitial fluid both connected (the contents of water, gas, electrolytes and small organic compounds are basically the same) and different (interstitial fluid contains very little protein). The relationship between the two is roughly equivalent to the relationship between rivers and groundwater. When the amount of river water rises, it will enter the ground and become groundwater; when the river water level decreases, groundwater will flow into the river to make up for the lack of river water; plasma proteins are centrally regulated to maintain blood osmosis. pressure, indirectly regulating blood volume.

River water and groundwater complement each other (picture source: tp.edu)

Blood cells are also constantly circulating, but the circulation of blood cells is not flowing, but "reconstruction and destruction." Reconstruction" style. White blood cells, red blood cells, and platelets all have a certain lifespan. Take white blood cells as an example. There are many types of white blood cells. Among them, neutrophils are the "vanguard" in responding to infections. The bone marrow produces neutrophils all the time, but only a small amount of these neutrophils enter the blood. After entering the blood, they stay in the blood for about 8 hours, that is, they enter the cell tissue. If no infection is encountered, these neutrophils will age and die after 45 days, and new neutrophils released from the bone marrow will fill their 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 this, we can analyze the remarks about voluntary blood donation.

Comment 1: Donating blood will affect immunity.

Wrong.

The human body’s immune system mainly consists of three parts: the barrier composed of skin and mucous membranes, the innate defense system composed of phagocytes, and the acquired immune system composed of B cells and T cells. Phagocytes, B cells, and T cells are all white blood cells. As mentioned earlier, white blood cells have a certain lifespan. At that point, the human body will destroy them. At the same time, hematopoietic tissues such as bone marrow are producing new white blood cells every moment.

So donating blood will not affect immunity.

Comment 2: Donating blood can cause fainting.

Yes.

Donating blood may indeed cause fainting, which is often referred to as blood donation reaction. In addition to fainting, blood donation reactions can also cause nausea, vomiting, paleness, palpitation, cold sweats, chest tightness and other symptoms. However, overall, the incidence of blood donation reactions is low, preventable, and has mild consequences.

According to a survey conducted by the Weifang Red Cross Center Blood Station, among more than 40,000 blood donations, only more than 1,000 cases of blood donation reactions occurred, 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 military personnel and medical workers are much lower than those of other occupations. This shows that mental factors play a decisive role in blood donation response. In addition, starvation, excessive fatigue or hot weather will also affect the incidence of blood donation reactions. Regardless of the cause, these patients returned to normal within minutes after receiving care. 3

Comment 3: People with high myopia cannot donate blood.

Controversial.

First of all, I checked the blood donation standards in the United States, Hong Kong and other places, and found no regulations that prohibit people with high myopia from donating blood. 4,5

Secondly, the old version of the "Health Examination Standards for Blood Donors" implemented in my country in October 1998 indeed stated that "patients with ophthalmic diseases, such as keratitis, optic neuritis and fundus height changes Myopia, etc." cannot donate blood.

However, in the 2011 version, which is the latest version of the "Health Examination Standards for Blood Donors", this was revised, these words were deleted, and only "those with active or progressive eye disease who have not recovered for less than 1 week shall undergo eye surgery". Those who have recovered less than 3 months ago are listed as those who are temporarily unable to donate blood.

The main difference between patients with high myopia (greater than 600 degrees) and patients with ordinary myopia is the front and back diameter of the eyeball. Ordinary myopia usually only involves abnormalities in the refractive system, while in patients with high myopia, the anteroposterior diameter of the eyeball usually becomes significantly longer.

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

The length of the front and back diameter of the eyeball can cause many consequences, such as fundus Change. Some studies have pointed out that the fundus blood flow in patients with high myopia will be reduced. Further examination showed that the blood vessels in the fundus of patients with high myopia become thinner. 6 Since blood vessels in the human body are interconnected, slight changes in blood pressure after donating blood may affect the blood vessels under the eyes, causing spasm of the blood vessels under the eyes, and increasing 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: staphyloma and atrophy (image source: pointsdevue.com)

Therefore, what affects blood donation is not high myopia, but changes in the fundus. The new version of "Blood Donor Health Examination Standards" also means this. Although high myopia has a high probability of being accompanied by fundus changes, it is not the only cause of fundus abnormalities. If conditions permit, it is best to conduct a fundus examination before donating blood; if conditions do not exist and you happen to be highly myopic, then, just to be on the safe side, you may not donate.

Comment 4: Donating blood multiple times can lead to obesity, increased blood pressure and other problems.

Wrong.

Since the human body can recover quickly after a single blood donation, and blood donation management organizations such as the Red Cross and the government have strict regulations on blood donation intervals, leaving sufficient recovery period for volunteers, then , Theoretically speaking, donating blood multiple times will not have any adverse effects on the human body.

Blood donation interval (picture source: "Health Examination Requirements for Blood Donors (2011)"

In fact, there is no evidence that multiple blood donations will affect health. However, some studies have pointed out that regular blood donation Donating blood can improve the blood sugar and blood lipid levels of volunteers. 7 However, the sample used in the study is relatively small, which means that it is unrealistic to improve health through regular blood donation.

Comment 5: You need to fast before donating blood.

Because going to the hospital for blood testing requires fasting, so many people think that you need to fast before donating blood. This is wrong. , blood donation reactions are more likely to occur when donating blood on an empty stomach; on the other hand, blood sugar and blood lipid levels are detected through blood tests. Blood sugar and blood lipids in the human body are not static, but are constantly fluctuating. Long-term fasting will cause blood sugar levels. , blood lipids are low, and after eating, these numbers will increase, and then gradually return to normal levels under the regulation of the human body. Therefore, in order to measure accurately, you should avoid blood sugar and blood lipids within 8 to 14 hours before checking. Eating.

This is not the case with blood donation. Volunteers donate blood for patients to use. Even if volunteers donate blood after eating, the slightly higher blood sugar and blood lipids will be absorbed by the patient's original blood. Dilution; even if the blood transfusion is large, as long as the patient's body's regulatory system is normal, blood sugar and blood lipid levels will still return to normal.

There is no need to fast for blood donation.

References

1Zhu Danian. Physiology[M]. People's Health, 2008.

2Li Yulin. Pathology[M]. People's Health Publishing House, 2008.

3Jiang Shuhua , Wang Lijuan, Ma Xueqin, et al. Analysis of causes and preventive measures of 1003 cases of blood donation reactions [J]. Chinese Journal of Blood Transfusion, 2001, 14(1): 4748.

4Eligibility Criteria:Alphabetical[EB/OL]. American Red Cross, [2018-02-26]. The signed articles published on this website only represent the views of the author and have nothing to do with this website. If there is any infringement, the author shall be solely responsible.

Author: Zhao Yanchang