The History of Blood Types

Blood has always had a mystical, life-giving quality to it, even in ancient societies. It is something worth protecting. Even today there are many terrifying stories across cultures of bloodsucking animals who prey on innocent humans in the night, either killing them outright or changing them into wicked creatures. Other real animals, mainly mosquitoes, are known to spread diseases such as malaria and West Nile virus via their bloody bites.

But this blog post isn't about blood diseases, though they are certainly worth a mention. It's instead about how science gained the basic understanding of blood and blood types and used it to save millions of lives.

A lab technician examining blood samples.
PC: iStock.com/Arindam Ghosh

Today, most people are aware that there are four blood types: A, B, AB, and O. Each person has one blood type, and for 99% of people, it's one of these. Some people are also aware of something called the Rh factor, which names a protein first found in a rhesus monkey in a laboratory (more on that later). 85% of people are Rh+ positive, and the rest are Rh negative. Except in very rare cases and in some pregnant women, Rh factor has no impact on a person's health. The way we talk about our blood types is putting the information about the type and the Rh factor together. For example, my blood type is A+, while my best friend's is O+. What makes my blood different from his?

It all comes down to something called antigens, which are sugars that exist on every single one of my red blood cells. Different blood types have different antigens in different places. For example, my A antigens are on my red blood cells, but I also have B antigens that exist in my plasma, the clear fluid that holds my red blood cells as well as other proteins and sugars that my body needs. A person with B blood has the opposite arrangement: B on the red blood cells, A in the plasma. Someone with AB blood has both A and B antigens on their red blood cells, and no antigens in their plasma, and someone with O blood has nothing on their blood cells and A and B antigens in the plasma.

Visualization of blood types.
From: https://www.redcrossblood.org/donate-blood/blood-types.html

Cool information, I guess, but what good does any of that knowledge do? Quite a bit, as it turns out! If someone gets a blood transfusion (a medical procedure where a patient receives blood from another human) and the blood type is not the same as theirs, there could be a potentially fatal reaction. Blood clots when it is mixed with an antigen it does not recognize. That's because foreign antigens trigger a response from a human's immune system, which is the system in our bodies that fights infection and sickness. Instead of helping the person by giving them blood, the new blood could actually kill them. Before 1900 and the discovery of blood types, a blood transfusion was a last-ditch effort in dying patients because it often resulted in the patient's death. No one knew precisely why.

The first blood transfusion was conducted in 1667 on a 15 year-old French boy by the physician Dr. Jean-Baptiste Denys. His early transfusions used animal blood instead of human blood, most often sheep but sometimes dogs. Patients who received large quantities of animal blood usually died after multiple transfusions, and today we can probably understand why: animals and humans have different blood types. Back then it was assumed that all blood was the same though, and sick people were willing to try anything to stay alive. Transfusion quickly was labeled so dangerous and controversial that in 1668 the French government and the Royal Society of London banned the procedure in their respective countries, and the Vatican condemned it in 1670. Transfusions were taboo for 150 years.

Physician James Blundell.
PC: engraving by John Cochran,
public domain.

In 1818, British physician James Blundell used a blood transfusion to treat a woman who had uncontrollable bleeding after giving birth. He may have been desperate to save her, even if the procedure was technically illegal. He saved her life, and decided to keep trying this technique on other patients. Out of ten transfusions he did in 1825 and 1830, five of them were successful and kept the patient alive. Even in the 1800s, this was a poor success rate, and the medical community viewed transfusions as risky and not medically sound. The procedure even made its way into horror literature: in Bram Stoker's Dracula, the character Lucy actually receives two blood transfusions from her suitors to replenish the blood Dracula has sucked away, but dies anyway. The death is attributed to the titular vampire, but I wonder if the transfusion itself didn't help advance her death.

It wasn't until 1900 that Austrian physician Karl Landsteiner noticed that blood from different humans would clump together when mixed (he also noticed the blood clumped when it was mixed with animal blood, which probably wasn't a surprise to him, given how many people had died from transfusions before). This was the first evidence of any difference in blood. He didn't yet know if the source of the differences was an inherent characteristic of the individual or the result of an infection acquired at some point in life. His experiments in 1901 showed that the blood of an individual would not clump with some people's blood, but would always clump with others. In this way he discovered the three blood groups, which he initially named A, B, and C. Group C would eventually be renamed after the German word for zero or null, ohne, and become what we call it today, O. Two of his students discovered the fourth main blood type, AB, in 1902.

Dr. Karl Landsteiner, blood type discoverer.
PC: The Rockefeller Archive Center.

 Though we today might think of blood types as basic information, especially given how many times it's mentioned in crime shows and medical dramas, this was a groundbreaking discovery in the early 1900s. Dr. Landsteiner refined his theory of blood groups and published it. The number of deaths from blood transfusions dropped dramatically after doctors learned to test blood before putting it into someone. Today it is one of the most common medical procedures, saving up to 4.5 million lives annually in the United States alone. For his discovery and work, and in recognition of the lives he had saved, Landsteiner was awarded the 1930 Nobel Prize in Medicine and Physiology. Landsteiner went on to discover the human Rh factor in 1937 by studying the similar antigen in the rhesus monkey.

Turns out there's a lot more to say about blood types and where they come from, so I'll continue that in next week's post. Until then, be safe and keep your blood where it belongs!