31 July, 2014 2:00PM AEST
A bloody mystery: why do humans have blood types?
By Matthew Bevan

Despite a century of study into blood types, scientists still don’t know what purpose they serve. What’s your blood type? Are you the universal donor O-? Or maybe you’re the universal recipient AB+.
Surprisingly, despite a century of study into blood types, scientists still don’t know what purpose they serve.
This week is the Australian Red Cross’s National Blood Donor Week, so Linda Mottram invited Professor John Rasko from the University of Sydney into the studio to find out what we know about blood, and how much remains a mystery.
When did we discover that there were different types of blood?
Since the turn of the 20th Century. Karl Landsteiner, an Austrian biologist and physician, won the Nobel Prize for the discovery of A, B and O main groups. In 1937 it was discovered that there are Rhesus positive and negative sub-groups, and since then we have discovered over 30 more blood groups. This makes the work of blood banks even more complicated.
Were transfusions attempted before Landsteiner’s discovery?
Yes. For centuries people attempted to use blood to treat people, mostly with fatal results. Pope Innocent VII was treated in 1492 with blood from four 10 year old boys. At the time the physicians were unaware that blood was circulating around the body from the heart, so the Pope drank the blood instead of injecting it. The Pope and all four of the boys died. In the centuries after, transfusions were attempted using both human and animal blood, but few were successful due to a lack of understanding of blood groups.
How exactly do the different blood groups present themselves?
Red blood cells have sugar coatings, carbohydrates or lipid molecules which act similarly to little hooks. Different configurations of these “hooks” are what denote different blood groups.
What function do they serve?
We do not know. Some blood groups actually are detrimental. For example the Duffy blood group makes your red blood cells more susceptible to malaria.
Does your racial background make you more likely to have a certain blood group?
Yes. African-Americans, originally from a place where malaria is endemic, has a lower incidence of the Duffy blood group.
What is the cause of your amount of haemoglobin dropping?
Haemoglobin dropping (otherwise known as anaemia) can be caused by many different things. Common causes are blood loss through the bowel, auto-immune attack, nutritional deficiency, vitamin B12 deficiency, iron deficiency and folate deficiency.
What is haemochromatosis?
It is an inherited condition which leads to an over-supply of iron in your blood. Treatment can include removing blood on a regular basis to make sure an iron overload doesn’t occur. In the past people with haemochromatosis were turned down by blood banks due to concerns about the quality of the blood, but that has changed. People with haemochromatosis who need to be regularly bled can donate that blood directly to the Red Cross.
Can you tell the parentage of a child based on blood groups?
In some cases. A parent with an AB blood type cannot have a child with an O blood type.
How many blood donations does the Australian Red Cross receive?
Australians give 27,000 blood donations per week. There are over 500,000 blood donors in Australia and 1.3 million donations per annum, but the Red Cross always need more donations.
Professor Rasko tested Linda Mottram’s blood type on air and found that it was O. What does that mean?
O blood is the absence of the A and B markers. This means O type blood can be donated to people with both A and B blood types.
Is there any truth to the theory that certain blood types should only eat certain foods?
No.