Blood Types Explained

by Jack Babbage

(Editor’s Note: The author of this article has just released a new book called, “The Pocket Encyclopedia of Emergency Preparedness” and will be an outstanding addition to your preparedness library. The book is like no other in the preparedness community, but once you look at it, you’ll understand that, not only did we need a book like this, but you’ll want it for your personal library. You can check it out on Amazon.


In 1901, Karl Landsteiner discovered that blood has distinct, incompatible types. Human blood was originally grouped into four types: A, B, AB, and O. O is written as the letter O, but it means zero (0), as in “none of the above”. The A and B designations refer to two kinds of antigens, or proteins, found on the surface of red blood cells. If, when examining blood under a microscope, A-antigens are visible, but not any B-antigens, then it’s type A blood. If neither A-antigens nor B-antigens are seen, then it’s type O blood.

Has A-antigens No A-antigens
Has B-antigens AB B
No B-antigens A O

In 1937, a third classification of human blood was discovered (while experimenting with Rhesus monkeys). This Rhesus factor, or “Rh factor,” is present (Rh+) in 85% of Americans. This is denoted by adding a “positive” to their blood type (A+, B+, AB+, or O+). For the 15% of Americans without it (Rh-), their blood type is “negative” (A-, B-, AB-, or O-). (By comparison, 99% of Chinese are Rh+.)

For a blood transfusion, you cannot give a particular antigen to someone who doesn’t already have it. Because O-neg blood has neither A, B, nor Rh antigens, it can be given to anyone. Someone who has O-neg blood is said to be a “universal donor,” although it’s not strictly true as there are other considerations that come into play under certain, rare circumstances.

Type U.S. Pop Who Can Receive
O+ 37% O+, A+, B+, AB+
O- 6% All blood types
A+ 34% A+, AB+
A- 6% A+, A-, AB+, AB-
B+ 10% B+, AB+
B- 2% B+, B-, AB+, AB-
AB+ 4% AB+
AB- 1% AB+, AB-
  • Blood type is inherited, like eye color.
  • Dogs have 4 blood types; cats have 11; cows have about 800.
  • Donated blood is subjected to four different sets of tests before it is declared safe for transfusion. Typing and cross-matching is only the first set of tests.


Ways to find out your blood type:

  • Your physician will have it in your chart if you ever received or donated blood.
  • An obstetrician will compare the mother’s blood type to that of the fetus.
  • If you have had surgery in the past, they may have checked your blood type beforehand as a precaution.
  • You can ask your doctor (or a local clinic) to perform a blood test directly, but you will have to pay for it directly as your insurance will not cover it without a medically necessary reason.
  • Donate blood and ask to be notified afterwards what your type is. (Be sure that they are willing and able to notify you. Some donation centers my have a policy against it.)
  • If you know the blood types of both of your parents, you can make an educated guess as to your own blood type. There are online calculators for this. Just be aware that genetics is sometimes whimsical; you may have inherited your blood type from a grandparent.


Jack Babbage is a semi-retired engineer and long-time prepper who dabbles in woodworking, leather working, electronics, and more. Read more about him at

This post is an excerpt from The Pocket Encyclopedia of Emergency Preparedness by Jack Babbage (July, 2019). There are over 650 articles like this one spanning 470 pages. It’s available from as a paperback and/or a Kindle eBook. Just search for Jack Babbage in the Books category and it will come right up.

This entry was posted in Books, Information, Entertainment and Plans. Bookmark the permalink.

One Response to Blood Types Explained

Join in on the discussion!