The ABCs of Blood Types: What Yours Says About You  

“Wait…blood has types?”

Yes, and while it’s all red…it is not all the same. There’s a whole sorting system that’s working behind the scenes, which determines who can donate blood to whom.

And guess what, it’s vital to know your blood type—it’s definitely more important than knowing your, say, I.Q.

As you’ll soon find out, in an emergency, it can be a matter of life and death. 

I. The Blood Alphabet: A, B, AB, and O

Almost half of Filipinos have “Type O” blood type.

That’s according to the Philippine National Red Cross.

  • 44-46% are Type O

  • 22-23% are Type A

  • 24-25% are Type B

  • 6-10% are Type AB

 So the rarest blood type is “AB.”

 But what do those mysterious letters mean—A, B, AB, and O?

They’re all about antigens. These are little protein markers hanging out on the surface of your red blood cells, kind of like name tags. Your immune system reads them and says, “Cool, you’re one of us.” But if it sees unfamiliar antigens—ones that shouldn’t be there—it freaks out and attacks.

So in short:

  • Type A has A antigens.

  • Type B has B antigens.

  • Type AB has both A and B antigens.

  • Type O has neither—completely antigen-free, like a blank name tag. 

These four types set the stage for whom you can donate to and receive from. And they play a key role in how your immune system handles transfusions.

But that’s not the full story yet. You’ve also got a plus or minus sign to deal with. 

II. The Rh Factor: Positive vs. Negative

You’ve probably heard it said, “My blood type is O+” or “She’s A-.”

What do the plus and minus signs mean?

That’s the Rh factor, short for Rhesus factor—a type of protein that’s usually found on the surface of your red blood cells. (Scientists call it the “Rhesus factor” because they first observed it in the Rhesus macaque monkeys they were studying.)  

  • If you have the Rh antigen, you’re Rh-positive (+).

  • If you don’t, you’re Rh-negative (–).

So, someone with A antigens and the Rh protein is A+, and someone without Rh is A-.

Why does this matter?

Because Rh compatibility can make or break a blood transfusion—or a pregnancy. Let’s say a Rh-negative person receives Rh-positive blood. Their immune system sees the Rh protein as an enemy and starts attacking it.

“Rh incompatibility” can happen during pregnancy. If an Rh-negative mother is carrying an Rh-positive baby, her body might treat the fetus like a threat, which is bad news for the developing fetus.  To prevent this, the mother is typically given a shot of immune globulin to prevent her immune system from developing antibodies against Rh+ cells.

So now that we know all this, let’s talk about who can safely give blood to whom. 

III. Donors and Recipients: Who’s compatible?

Combining two types of Rhesus factors (positive or negative) and the four blood types (A, B, AB, and O), we now have 8 types of blood.  

You know, before they discovered the different blood types, doctors were wondering why some blood transfusions were successful but others were not.

The successful ones usually had no incidents. 

The failures had displayed clumping and clotting. (Uh oh!) This means the recipient’s blood is reacting negatively to the transfused blood and is attacking it. Antibodies in the recipient’s plasma bind to the antigens in the donor blood, causing them to clump.

This can lead to a host of complications like blocked blood vessels, hemolysis, shock, kidney failure and even death.

But don’t worry, blood transfusions these days are very safe, and have loads of redundancies and safety protocols so shocks do not happen.

The A-B-O blood types that we know today are all thanks to the Austrian pathologist and biologist Karl Landsteiner, who discovered them in 1901 (for which he later won the Nobel Prize). 

Each blood type has specific compatibility rules. Some types are generous givers, others are picky takers.

So now, let’s look at the combos allowed.

Who Can Donate to Whom?

Here’s the quick compatibility rundown:

  • O- is the universal donor. Meaning, it can donate to all blood types. It has no A, B, or Rh antigens, so it’s the safest bet when you don’t know someone’s blood type. Basically, the Switzerland of blood types—neutral and lifesaving.

  • AB+ is the universal recipient. Meaning, it can receive blood from anybody. It has all the antigens (A, B, and Rh), so it’s used to everyone. No drama.

 

Now, let’s match the rest:

  • O- can donate to anyone.

  • O+ can donate to O+, A+, B+, AB+.

  • A+ can donate to A+ and AB+.

  • A- can donate to A-, A+, AB- and AB+

  • B+ can donate to B+ and AB+.

  • B- can donate to B-, B+, AB- and AB+

  • AB+ can only donate to AB+.

  • AB- can donate to AB+ and AB-

 

Who Can Receive What?

  • If you’re O-, sorry—you can only receive from O-. You’re rare and selective.

  • If you’re O+, you can receive from O+ or O-.

  • If you’re A+ you can receive from A+, A-, O+ and O-

  • If you’re A-, you can receive from A- and O-

  • If you’re B+ you can receive from B+, B-, O+ and O-

  • If you’re B-, you can receive from B- and O-

  • If you’re AB+, lucky you. You can receive blood from any type.

  • If you’re AB- can receive from A-, B-, AB-, O-.

 

Hospitals keep “O-“ blood bags on hand like gold. In trauma cases where there’s no time to check blood type, O- steps in as the universal emergency donor.

So yeah—blood isn’t just red stuff. It’s a system. A network of immune recognition, compatibility, and trust. One wrong match, and the immune system gets into action.

And that is still not the full story.


IV. Our Sons & Daughters

Did you know that blood types are inherited?

Children combine the Rh factors of their parents to determine if they ultimately are Rh+ or Rh-.

The positive (+) allele is dominant, and the negative (-) allele is recessive.

So a person with two positive alleles (++) will be Rh+. And because the positive allele is “dominant,” individuals with at least one positive allele will be Rh-positive. Only someone with double negative alleles (−−) will end up Rh-negative. This explains why there are more Rh+ people than Rh-. 

Each person also inherits their parents’ blood types (A, B, or O) and combines them to determine their ultimate blood type. An individual, for example, who received “A” from both parents (AA) will obviously be type A.

A and B are dominant, while O is recessive. This means if someone has an A and an O (AO) inherited combo, that individual will ultimately have type A blood. Somebody with a BO parental combination will ultimately have type B blood.  

Only someone with double O alleles (OO) will have type O blood.

Now, as a parent, if you’re “type A”, it doesn’t automatically mean you only pass on “A” blood. That’s only true if you’re double (AA) yourself. You could very well be an AO, which means, even though you are type A, you can pass on “O” to your offspring.

So if one parent is type A (with genotype AO) and the other parent is type B (with genotype BO), their child could be type A, B, AB, or O, depending on which alleles are inherited.

Here’s a table of the different possible combinations.

 Source: www.https://www.ncbi.nlm.nih.gov/

Notice that if both parents are type O (OO), the child will always be type O.

There’s this common trope in medical dramas where an individual discovers inconsistencies between his parents’ blood types and his own—leading to the realization that he was adopted.

 

Our blood carries a ton of information about us.

A simple vial of blood holds a staggering amount of information about our health. Beyond determining paternity or blood type, blood tests can uncover hidden issues, track the progression of disease, and help guide life-saving treatment decisions.

High blood sugar levels, low RBCs, or high WBCs can indicate something you need to pay attention to. But we need to go back to basics and know the most fundamental thing: one’s blood type. That knowledge can come in handy in medical emergencies and the like.

So…what’s your type?

 

BloodWorks Lab can help determine not just your blood type, but a host of other data about your health. We are your one-stop shop for all your blood test needs, offering checkup packages tailored specifically for you.

We are the first in the country to offer the Anti Acetylcholine Receptor (IgG) Antibody Test and the Anti N-Methyl-D-Aspartate Receptor (Anti NMDA Receptor) Antibody Test.

Book your appointment today.

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