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Ever get the feeling sometimes that everybody's after your blood? Well, if you happened to be at Wynberg Girls' High on the morning of February 3, they were, when one of the quarterly blood clinics were held. Students over 16 and weighing more than 50kg were invited to participate in this invaluable service to the broader community.

A few facts about blood: ¹

We all have these little markers antigens on the surface of our red blood cells. These are so tiny they can't even be seen under a microscope.Everyone's got different ones except identical twins who possess the same antigens. When it comes to blood transfusions, there are two very important systems of antigens which need to be matched to avoid any nasty complications.

The ABO System

If you have blood group A then you've got A antigens covering your red cells. Blood group B means you have B antigens, while group O has neither, and group AB has some of both. The ABO system also contains lots of little antibodies in the plasma, antibodies being the body's natural defence against foreign antigens. So blood group A has anti-B in their plasma, blood group B has anti-A.To complicate matters though, group AB has none and group O has both of the antibodies. Which means giving someone blood from the wrong ABO group could be fatal. The anti-A antibodies in group B attack group A cells and vice versa. Which is why group A blood must never be given to a group B person.

It gets more complicated because there's another antigen to be considered - the Rh, (or rhesus) antigen. Some of us have it, some of us don't. If it is present, the blood is RhD positive, if not it's RhD negative. So, for example, some people in group A will have it, and will therefore be classed as A+ (or A positive). While the ones that don't, are A- (or A negative). And so it goes for groups B, AB and O. This effectively doubles the number of different blood types to be matched, because you shouldn't mix blood type A+ with blood type A-.

The average blood group distribution in South Africa is

38,5% or O Positive (1 in 3);
A positive is 30,4% (1 in 3),
B Positive is 15,8% (1 in 6) while less common is
AB Positive at 4,4% (1 in 23).

Also scarce is O negative at 4,5% (1 in 22);
A Negative at 4,1% (1 in 24),
B Negative at 1,6% (1 in 62) and
AB Negative at 0,6% (1 in 167).

O negative is an especially important blood type. Mainly because it can be given to anyone, regardless of what blood group they have. O negative is also vitally important for specialised procedures, like giving an unborn baby with a blood disease a transfusion in the womb. It can also help prevent brain damage in a newborn baby suffering from jaundice. And it's the blood used most frequently for patients receiving bone marrow transplants.

So although it might be called negative, this particular blood group is anything but.

¹
information obtained from the National Blood Service
website for England and North Wales

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This page was last updated on 04 February 2003 06:02