A blood type is “positive” when red blood cells carry a specific protein called the RhD antigen on their surface. About 85% of people worldwide are Rh positive, and it only takes one copy of the Rh-positive gene from either parent to produce a positive blood type. The “positive” or “negative” label applies to all four ABO groups, giving you the familiar types: A+, B+, AB+, and O+.
What Makes Blood “Positive”
Your blood type has two parts. The first is your ABO group (A, B, AB, or O), determined by which sugar molecules sit on the surface of your red blood cells. The second is your Rh factor, determined by whether your red blood cells carry the RhD antigen, a protein encoded by a gene on chromosome 1. If that protein is present, your blood type gets a “+” after it. If it’s absent, you’re negative.
So A positive means your red blood cells have both the A antigen and the RhD protein. O positive means you lack A and B antigens but do have the RhD protein. The “positive” part is always about that one protein.
How You Inherit a Positive Blood Type
The Rh-positive gene is dominant. That means it overrides the Rh-negative gene whenever both are present. You inherit one Rh gene from each parent, giving you one of three possible combinations:
- Two positive genes (+ +): Your blood is Rh positive.
- One positive, one negative (+ -): Your blood is still Rh positive, because the positive gene is dominant.
- Two negative genes (- -): Your blood is Rh negative. This is the only way to be negative.
This means a person who is Rh positive might carry a hidden negative gene. They could pass that negative gene to a child without ever knowing they carried it.
Parent Combinations That Produce Positive Blood
Several parental pairings can result in a positive child. Here’s how it breaks down:
If both parents are Rh positive and both carry two positive genes (+ +), every child will be positive. If both parents are positive but one or both carry a hidden negative gene (+ -), most children will be positive, but there’s a 25% chance of a negative child when both parents are carriers.
If one parent is Rh positive and the other is Rh negative (- -), the outcome depends on whether the positive parent is + + or + -. A parent with + + will always pass on a positive gene, so the child will always be Rh positive. A parent with + – has a 50/50 chance of passing either gene, so roughly half their children with an Rh-negative partner would be positive and half negative.
Two Rh-negative parents (both – -) can only produce Rh-negative children. Neither parent has a positive gene to pass on.
How Common Positive Blood Types Are
Rh-positive blood types are far more common than negative ones. According to NHS Blood and Transplant data from 2026, roughly 77% of donors are Rh positive. The breakdown across all eight common blood types looks like this:
- O+: 36%
- A+: 28%
- B+: 8%
- AB+: 2%
- O-: 14%
- A-: 8%
- B-: 3%
- AB-: 1%
O positive is the single most common blood type, while AB negative is the rarest.
Transfusion Compatibility for Positive Types
If you’re Rh positive, your immune system already recognizes the RhD protein as normal, so you can safely receive both Rh-positive and Rh-negative blood (as long as the ABO group also matches). An Rh-negative person, on the other hand, can react to Rh-positive blood because their body sees that protein as foreign.
Here’s what each positive blood type can receive:
- A+: Can receive A+, A-, O+, O-
- B+: Can receive B+, B-, O+, O-
- AB+: Can receive all eight blood types (universal recipient)
- O+: Can receive O+ and O-
Why Rh Status Matters in Pregnancy
Rh factor becomes especially important when a mother is Rh negative and her baby is Rh positive, having inherited the positive gene from the father. During delivery, or sometimes during pregnancy itself, a small amount of the baby’s blood can enter the mother’s bloodstream. Her immune system recognizes the RhD protein as foreign and begins producing antibodies against it.
This usually doesn’t cause problems in a first pregnancy because the antibody response is slow to build. The risk comes with future pregnancies. If a second baby is also Rh positive, those antibodies can cross the placenta and attack the baby’s red blood cells. This can cause severe anemia, jaundice, and in serious cases, can be fatal. Blood mixing can also happen after a miscarriage, ectopic pregnancy, or certain prenatal procedures like amniocentesis.
Doctors routinely test Rh status early in pregnancy. If a mother is Rh negative, she receives an injection that prevents her body from making anti-Rh antibodies, effectively neutralizing the risk before it starts.
How Your Blood Type Is Tested
Blood typing is a simple lab test. A technician takes a small sample and mixes it with three different reagent solutions: one containing anti-A antibodies, one with anti-B antibodies, and one with anti-D (Rh) antibodies. If your red blood cells clump together when exposed to the anti-D reagent, you’re Rh positive. If they don’t react, you’re negative. The whole process takes minutes and is standard practice before transfusions, surgeries, and during prenatal care.