Blood. What does it have? Why donating blood is so important?

On the 14th of June is the World Blood Donor Day.

But, as always, let’s start from the beginning.

What is the blood and why it is important?

Our body is made up of cells. All kinds of cells. When we have many similar cells that have a specific function, we form a tissue. And when we have different tissues, we form an organ, like the skin, the stomach, the heart…

Blood is a tissue, even though it’s liquid. More specifically, it’s connective tissue. It’s composed of plasma and cells that travel within it, such as red blood cells, white blood cells, and platelets. An adult person has between 4 and 5 litres of blood circulating in their body.

Plasma is mostly water, but it’s also made up of the nutrients we eat, carbohydrates in the form of glucose, proteins, fats, vitamins, and minerals, as well as hormones.

Blood has three main functions:

Transport: Blood carries nutrients from food and oxygen from respiration to all body parts. It also removes waste products, such as carbon dioxide, to organs responsible for eliminating them. It also transports hormones.
Regulation: Blood maintains our body temperature, pH balance, and the amount of water in our cells stable.
Protection: Blood defends us against infections, and its clotting ability prevents excessive bleeding when we are injured.

Now, let’s take a look at the cells present in this tissue:

Red blood cells:

Also called erythrocytes. They are biconcave discs, like two shallow bowls joined together at the bottom.

Each side fills with oxygen in the lungs and carries that oxygen to the rest of the body. This process is facilitated by haemoglobin. When the blood returns to the lungs, red blood cells carry the carbon dioxide we have produced to be expelled.

Also, red blood cells have antigens on their membrane, their outermost part, like antennas, which tell us what blood group we belong to. That is, A, B, AB, or O.

If the red blood cell has “antennas” of type A, our blood group is A; if it has “antennas” of type B, our blood group is B. If it has both, we belong to blood group AB, and if it has none, we belong to blood group O.

Red blood cells also determine our Rh factor, whether it is positive or negative. All this information defines who we can donate blood to and who we cannot.

White blood cells, or leukocytes:

Those cells are the ones that help us fight microorganisms such as viruses, bacteria, fungi, and parasites, meaning they combat infections. They also eliminate substances and even cells from our own body that may be dangerous, such as cancerous cells or dead cells.

There are many types of white blood cells, and each one has a specific function when it comes to attacking these microorganisms or cells. They can activate the immune system, attack them to prevent harm, or even “eat” them. There are 5 types of white blood cells: monocytes, neutrophils, lymphocytes, eosinophils, and basophils.

Platelets, or thrombocytes:

These blood components don’t quite reach the level of being cells themselves. Their function is clotting, which means stopping blood loss when a wound occurs, such as when a blood vessel (an artery, a vein, etc.) is broken. Platelets gather and adhere to the wall of the blood vessel to plug the gap left by the wound and prevent blood from leaking out.

Donation:

Now that we know a little more about blood, let me explain how blood donation works.

A person with blood type A can only receive blood from another person with blood group A. The same goes for a person with blood type B; they can only receive blood from people with blood group B. People with blood group O can only receive blood from individuals with blood type O. However, they are called universal donors, meaning they can donate blood to individuals with any blood group (A, B, AB, or O).

And… is there anyone who can receive any type of blood?

Yes, people with blood group AB. They can receive blood from individuals with blood group A, group B, group AB, and group O.

However, blood is not that straightforward, and it needs to be studied before donation to ensure compatibility between donors and recipients.

What I mean by this is that blood donation isn’t just about those little A and B antigens on red blood cells I mentioned before. It also depends on whether red blood cells have other antigens, let’s call them “flags,” to distinguish them from the “antennas” mentioned earlier.

Well, there are people whose red blood cells have these “flags”, which are called Rh positive (Rh+) and people who don’t have these “flags,” which would be Rh negative (Rh-).

Taking all of this into consideration, we actually have 8 blood types: A+, A-, B+, B-, AB+, AB-, O+, and O-.

People with negative blood type can donate to people with positive blood type, but not vice versa. That is, A- can donate to both A- and A+, but A+ cannot donate to A-.

Compatibility among blood groups. Source: Red Cross.

And after all that… how does blood donation work?

When we donate blood, we usually have a needle connected to a bag that fills up over time. Later, in the laboratory, that blood is divided into three other bags, each containing a component of the blood: plasma, red blood cells, or platelets. Each one is stored and preserved differently.

There is another type of donation called apheresis, where the blood is separated into its components directly in the bag being filled when we are punctured, without having to go to the laboratory. It is used to extract only one of the components needed, for example, red blood cells. The red blood cells remain in the bag, and through another needle, the blood that has not been stored in the bag re-enters our body.

With a single blood donation, you can help up to 3 people, as each component is used for different purposes. And beware! Blood, even when refrigerated, has an expiration date. That’s why donations are needed all the time.

Red blood cells “expire” after 42 days, plasma after 2 years, and platelets can only be stored for 7 days, and they must also be stored in a machine that constantly moves the bags.

Some examples of their use:

Red blood cells are used in surgeries where blood loss occurs or in complicated childbirths, platelets are used in people undergoing treatment for blood cancer (leukaemia), and plasma in transplants.

The blood separated into different properly labelled bags is stored. Each type of component must be kept cold at a different temperature.

Who can donate blood?

All individuals between 18 and 70 years old, weighing at least 50 kilograms, and in good health can donate blood.

Women can donate during menstruation; there is no issue with that.

There might be some cases where you can’t donate:

According to the Irish Blood Transfusion Service: https://www.giveblood.ie/can-i-give-blood/faqs/health-faqs/

According to the WHO, one should wait a minimum of 9 months after childbirth and 3 months after finishing breastfeeding.

We should also wait if we have any illness caused by respiratory viruses such as SARS-CoV-2, the flu, or any other infection. If we have gotten a tattoo or piercing, we should wait for 4 to 6 months (depending on the donation centre). If we have undergone a minor dental treatment, like a filling, we need to wait for 24 hours, and if we have recently travelled to areas where diseases are transmitted by mosquitoes, we should also wait for some time before donating blood. You have more info in the references and you can always check the guidelines of the blood donation centre in your city.

IMPORTANT:

Do not donate on an empty stomach. This is not a blood test, and they will draw almost half a litre (about 470 mL). Go well-fed and, above all, well-hydrated. Drink water before and after to help replenish the fluid that will be drawn from you.

However, at your donation centre, you will receive further guidance on all this information (how to prepare before and after donation), and they will assess whether you can donate or not based on each individual’s circumstances.

References:

Book principles of anatomy and physiology Tortora & Derrickson

https://www.donaprinciplessang.org/que-es-la-sang/es_index.html

https://www.texasheart.org/heart-health/heart-information-center/topics/blood-cells/

https://www.msdmanuals.com/home/blood-disorders/biology-of-blood/components-of-blood

https://www.carterbloodcare.org/education-center/blood-types/

https://www.medicalnewstoday.com/articles/es/tipos-de-sangre#que-es-un-tipo-de-sangre

https://www.who.int/es/campaigns/world-blood-donor-day/2021 https://donarsang.gencat.cat/es/puedo-donar/

https://www.who.int/es/campaigns/world-blood-donor-day/2020/who-can-give-blood

https://www.mayoclinic.org/es-es/tests-procedures/blood-donation/about/pac-20385144

Images:

https://pixabay.com/photos/blood-donation-donate-plasma-donor-5053760/