A, B, AB or O? Rhesus-positive or negative? Many people don’t know their blood type.
While it isn’t always necessary, in some cases, like when pregnant, it's prudent to know it so you will be able to understand - and double-check - what the doctor does.
Besides, it couldn’t hurt to know, said Birgit Stuermer, a phlebotomist with the German Red Cross.
How do you determine your blood type?
Every time a donor gives blood, the blood type will be tested to ensure no mistakes are made and it is classified correctly. Most donation centers will issue an ID card that states which one of the three blood types a donor belongs to.
The card also states whether you are positive or negative for the rhesus and Kell antibodies.
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Does it help to know your blood type in an emergency situation?
Some people think that in emergency treatment they’ll be able to receive blood more quickly than someone who does not know their blood type.
This isn’t the case. Before every blood transfusion the blood type will be routinely checked by a scientific means, Stuermer said.
"The information on the card does not suffice legally," she said.
When is it especially worth knowing your blood type?
When a woman is pregnant, a doctor will have to determine if there is any blood incompatibility between mother and child and may want to discuss this.
When it occurs, the mother's blood cells develop antibodies that can attack the newborn's blood and cause jaundice.
Also, knowing the blood type can have a societal benefit.
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For example, people with blood type O comprise only 6 per cent of the population, but their blood can help a lot of people.
"This is universal donor blood," Stuermer said. The AB blood type, on the other hand, is popular for plasma donations, as it can be transfused to any patient.