Do you ever stop and think about how weird it is, that you can give complete strangers your blood, I mean, this isn't like lending someone your jumper here, is it’ this is your own precious life force right?

The modern world has made it so easy to save someone's life with something that your body makes for free.

So, let's first talk through what happens when you donate, then get to the interesting stuff about where your blood goes afterward and then why those A+ positive and O- negative scores really mean so much.

So, giving blood once you reach the age of 17, you're eligible to donate. When you arrive nervously looking around for vampires, you'll have a form to fill in and a chat with a carer to check that everything is alright. Then also test your hemoglobin levels by putting a drop of your blood in a copper sulfate solution to look at the density of your blood, a test that was actually invented for soldiers in World War II.

If you've got blood, that's full of iron, if you've been eating your spinach, you'll move on to the donation itself, you lie back in a chair they put a cuff on your arm to create a little bit of pressure and they insert the needle which is already attached to a tube that leads to your own personalized blood bag, lovely’.

 As the blood leaves your body, it fills the bag which rather helpfully contains anticoagulants to stop its clotting. It also sits on a scale so it can automatically stop the donation when you've given it just under a pipe, important to avoid draining you dry.

The average person has about eight pints of blood in them, so as long as you drink some water afterward you can easily make up the volume.

 After all, you make two million red blood cells every second and the whole thing usually takes five to ten minutes, and it's so uneventful that a lot of people play candy crush during the whole thing.

 After the donation, you go off for some squash and a biscuit and the real work begins, your bag is carted away to a blood bank, where it's tracked by barcode and hung up on machines, inspired by fish smoker ease. Some of these banks hold more than 1,000 gallons of blood that's enough to fill around 56 bathtubs.

 Blood donations have to be processed immediately as the red blood cells will only last around about 35 days and other blood components last even less time, if the blood of a special type or group is needed then they can actually rush out in under an hour which means we should chat about blood type.

 You have the same blood group your whole life, it's nothing like an exam grade, and the letter and a positive or negative sign refers to the protein molecules on the surface of your red blood cells, they're called antigens and that means any substance that potentially causes a body to produce an immune response to it, now in their case, these are your personal self-antigens and your body just ignores them. You can have up to 342 (three hundred and forty-two) types of antigens on your red blood cells and because lots of us share a whole bunch of them we divide blood into a few different groups based on those differences A, B, AB, and O are the most common letter grades.

 Now around 48 percent of the UK the population has group O, 39 percent A, 10 percent B, and 3 percent AB, then you get variants of these like O+ which is for people who don't have any of the A or B antigens but they do carry some rhesus group antigens, RH's, and yep they're named rhesus because they were discovered in rhesus monkeys. RhD is the most common of the RHS making O+ the most common blood group in the UK, with 36% of the population having RhD antigens but not A or B

 If you get blood with the wrong antigens or accidentally took on monkey blood, your body's immune system would flag your blood as not being your own and start attacking it, actually bursting the red blood cells open, that's why every single donation is important. People need an exact match.

 Because your blood group is genetic, a match is more likely to come from people from within your own ethnic background, if you're from an ethnicity that is in a minority, there may be less blood available for people with your blood type, which is why donating is super important and that's why O- negative which we used to call the universal donor, is such a useful blood type in an emergency it can be given to almost anyone. That doesn't mean that O- negative has no antigens it's just lacking those RhD ones which are the most immunogenic, they're most likely to cause an immune reaction in a patient, there are still around 50 RH antigens that they could have.

The closest the thing we know to a true universal donor is the 40 or so people in the world with golden blood. It's still red of course but it's Rhnull, they have no antigens from the rhesus group at all and the amazing but the sad thing is that these people of golden blood can save almost anyone's life but they have to live really carefully themselves because if they did have an accident the only blood transplant that they could take would be from a fellow person of rare golden blood.


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