[HPsquared]

There are three components that can cause problems with transfusions: "A", "B" and "Rhesus". A person can have any combination of those three (8 combinations).

The A/B/AB/O is basically having only A, only B, both, or neither. And the +/- is whether you have the "Rhesus" component.

The basic rule is that you can't introduce new components to a person who doesn't have them in their system, and will be treated as foreign contaminants.

So someone with all three components already (AB+) can take any blood because their system already is used to all three components.

A person with none of the components in their system (O-) would have an allergic reaction to any of the three components being introduced. On the other hand their blood is safe to donate to anyone else as it won't introduce any "unexpected components" to a recipient.

EDIT: ah, I see - article doesn't mention Rhesus. I guess it can convert AB- to O-, or AB+ to O+.

[Buttons840]

I think O is recessive (if I remember from high school correctly).

A is really AO (if we're being verbose). B is BO, AB is AB, O is OO. Each parent passes one of them on. So, a A dad and O mom would mix (being verbose again) AO and OO, and thus the child might be AO or OO, A or O.

The + or - is for an independent "Rhesus" component, as you say. Not sure how this passes through the genes. This is all like high school level knowledge, so maybe someone can share more if they want.

My dad had surgery and some paperwork we received said that he had AB blood. It became a family joke because me and my siblings are all O blood type. If my dad really did have AB blood then we are not his children. The hospital later confirmed it was a mistake.

[blendergeek]

You mostly remember correctly. One small nitpicko on the genetics (based on my high school biology)

A can be either AA or AO and B can be either BB or BO.

AB is always AB like you said and O is always OO.

[linooma_]

> I think O is recessive

Strangely, O is very common.

[thaumasiotes]

What's the strange part? "Recessive" and "common" are different concerns.

Having five fingers per hand is recessive too.

[quesera]

> Having five fingers per hand is recessive too.

Fascinating, and true.

Which engenders speculation about how the world would be different if we counted in base-12. Obvious advantages to convenient divisibility aside.

[thaumasiotes]

It wouldn't be different at all. Mostly we did use units of twelve for everything. Why do you think there are twelve inches in a foot and twelve pence in a shilling?

Asking what the historical difference would be if we wrote our numbers in base 12 instead of, variously, 10, 12, or 20 (all historically common, and 60 is prominent too), is like asking what the historical difference would be if we wrote our words in Greek letters instead of Roman letters.

Note that it was common for people to count dozens on their hands; each hand has four non-thumb fingers with three knuckles each.

[quesera]

Of course it would be different. I'm well aware of historical numbering systems, and their applications.

My point is that if base-12 was biologically natural, instead of more effortfully useful, there would be many differences in the way we do things -- although of course we would be mostly unaware of them, as a fish in water.

There would be no metric-vs-imperial units dichotomy, for example. (EDIT: Or at least the conflict would be different and likely lesser, ergo easier to switch)

NASA probably wouldn't have lost the $327MM Mars Climate Orbiter. And it wouldn't have cost $327MM in the first place.

In some cases, unit sizes would be different. That's the easy case. But in counting systems, 100 of some atomic thing would be 44% more than it is today. 1000 would be 73% more. 1MM would be almost triple. Given the attachment people have to round numbers, this would have implications. Some things would be bigger. Other things would be considered in different increments.

It's interesting. Not profound.

[riffraff]

I seem to remember the explanation is that A and B are somewhat recent mutations in evolutionary terms, they simply have not had time to cancel out 0 yet.

Of course there's crackpot theories (aliens!) too.

[jorvi]

Also important to note that blood plasma is the reverse. So AB+ is universal plasma donor, and O- universal plasma receiver!

[wbl]

Oh there are more. I think hundreds are known, but only a few populations have each one.

[smegger001]

there is also the HH blood group that will react negatively to O type blood as well as A and B.

[Terr_]

That naming is a little confusing, because if you say "blood group "A" or "B", that indicates the presence of A and B antigen structures, however "blood group H" means a lack of H. (Since almost everybody has H, it was discovered much later.)

Since H is also a building-block needed for A and B to show up, it makes for fun medical-mystery plots, where a child's blood-type seems to be O and doesn't match their parents, but in reality they did get parental A/B/AB genes that just aren't able to express because each parent contributed a nonfunctional H-allele.

https://www.ncbi.nlm.nih.gov/books/NBK2268/

[Terr_]

P.S. IANAPhlebotomist, but if I could wave a wand to change the nomenclature, I'd make it stop relying on an implicit "nothing" state that keeps changing under us as we discover new features that are either usually-present or usually-absent.

Instead patients would have a "blood code" that indicates the tested presence or absence of phenotype cellular features, and any feature not listed would be considered "not yet known, do a test if it might be important."

For example, today's AB- would become +HAB-R for "has H,A,B lacks Rhesus factor." Similarly, O+ would become +HR-AB, and the super rare mutation we were just talking about would be either +R-HAB or -HABR.

Then when we eventually discover a yet-another factor X... Well, yes, your code wouldn't be constant throughout your life, because after an X-test it would gain either a +X or -X... However the upshot is that it eliminates weird implicit guessing games, and medical professionals will "know what they don't know".

[thaumasiotes]

> For example, today's AB- would become +HAB-R for "has H,A,B lacks Rhesus factor."

That's already the way A, B, and Rhesus factor work. The abbreviation for Rhesus factor is "+", but the formal terminology is "Rh+". I would have expected "H-" by analogy.

[Terr_]

> That's already the way A, B, and Rhesus factor work.

No, it isn't: The current ABO system is incapable of expressing "null" data (e.g. "we don't know if B antigens are present or not") and relies on implicit "no marking means false" assumption, which becomes a problem if a new/newly-important antigen feature is discovered, or if a new variation of an existing antigen is found.

For example, suppose we discover a new type Z, which is a membrane-sugar just like A and B, and logically ought to be encoded the same way. It exists in a 50/50 ratio in every existing blood-group, and it finally explains some rare but fatal transfusion problems.

Now some unconscious patient arrives at the emergency room with a wristband saying "AB+". Does that string mean they were tested for Z already, and it was absent, or does it mean there no data about whether Z is present or not? Nobody knows! Worse, if you do a test and discover no Z, then you write the same thing and have the same problem later, all because of the mistake of encoding "false" as an empty string.

Now you might say "Forget the ABO crap, require Z+ or Z- to appear as a separate item", I'll say: "I totally agree, but let's remove the ABO crap and encode all the antigens the same way to make it logically consistent and clear."

> I would have expected "H-" by analogy.

If you're thinking of another section like "A Rh+ H-", then that's close to what I'm proposing, except that it hasn't fixed the historical ambiguities of O/A/AB.

If you fix it to make things explicit and consistent, it becomes "A+ B- Rh+ H- ", and if you shorten Rh to R and group similar things together... that leads to codes like +R-HAB or -ABH+R, which are (ordering aside) what I just proposed.

[Sn0wCoder]

I have never heard of the H-allele. Not sure if @Buttons840 has seen this but “It became a family joke because me and my siblings are all O blood type. If my dad really did have AB blood then we are not his children. The hospital later confirmed it was a mistake.”

Thank you for the information as I always love learning more from the comments than the articles.