A positive (A+) is the second most common blood type in the United States, found in about 35.7% of the population. If you’ve just learned your blood type is A positive, it means your red blood cells carry two key markers: the A antigen on their surface and the Rh protein (also called the Rhesus factor). Here’s what that means for your health, your family, and situations where your blood type actually matters.
What Makes Blood “A Positive”
Your blood type is determined by two separate systems working together. The first is the ABO system, which looks at which antigens sit on the surface of your red blood cells. You have the A antigen, which means your immune system recognizes A-type cells as its own but produces antibodies against B-type cells. This is why receiving the wrong blood type can trigger a dangerous reaction: your body attacks the foreign cells.
The second system is the Rh factor, a protein also found on the surface of red blood cells. “Positive” means you have this protein. About 85% of people are Rh-positive. The Rh protein doesn’t affect your day-to-day health. It only becomes important in two situations: blood transfusions and pregnancy.
Who You Can Donate To and Receive From
For red blood cell transfusions, compatibility depends on matching antigens. Because your cells carry the A antigen and the Rh protein, you can receive red blood cells from four blood types: A+, A-, O+, and O-. You can donate red blood cells to people with A+ or AB+ blood.
Plasma works in reverse. Your plasma contains antibodies against the B antigen, so it can only go to recipients who don’t have B-type cells. That limits your plasma donations to people with type A or type O blood. People with AB blood, by contrast, make no antibodies against A or B, making their plasma universally compatible.
A+ blood is in high demand at hospitals. It makes up almost a third of all blood requests, and A+ platelets are issued to hospitals more frequently than platelets from any other blood type. If you’re considering donating, your blood type is one that blood banks consistently need to keep stocked.
Health Risks Linked to Type A Blood
Blood type has a small but measurable connection to certain health conditions. A study tracking 89,500 adults over 20 years, conducted through Harvard’s School of Public Health, found that people with type A blood had a 5% increased risk of coronary heart disease compared to those with type O. That’s a modest bump, not a dramatic one, and lifestyle factors like diet, exercise, and smoking still dwarf blood type as predictors of heart disease.
There’s also a connection to stomach cancer. Research has shown that individuals with blood type A have about 1.34 times the risk of developing gastric cancer compared to people with other blood types. Scientists believe this may relate to how the A antigen interacts with certain bacteria in the stomach lining, though the exact mechanism is still being studied. Neither of these associations is large enough to change your screening schedule or warrant anxiety, but they’re worth knowing as part of your overall health picture.
Pregnancy and Rh Factor
Being Rh-positive is the easier scenario for pregnancy. The main Rh-related complication, called Rh incompatibility, happens when an Rh-negative mother carries an Rh-positive baby. In that case, the mother’s immune system can develop antibodies against the baby’s blood cells, potentially causing serious problems in future pregnancies. These mothers receive a preventive injection (commonly known as RhoGAM) around 28 weeks and again after delivery.
If your blood type is A+, you won’t need this treatment. Your body already has the Rh protein, so there’s no mismatch to trigger an immune response against an Rh-positive baby. And if your baby happens to be Rh-negative, that doesn’t create a problem either, because the issue only runs in one direction.
How A+ Blood Is Inherited
Blood type is genetic, determined by genes you received from both parents. The ABO part and the Rh part are inherited independently, controlled by different genes.
For you to have type A blood, at least one parent needed to pass along an A gene. Several parental combinations can produce a type A child:
- A + A can produce A or O
- A + B can produce A, B, AB, or O
- A + AB can produce A, B, or AB
- A + O can produce A or O
- AB + AB can produce A, B, or AB
- AB + O can produce A or B
For the Rh-positive part, at least one parent needed to carry a positive Rh gene. Two Rh-positive parents can have either a positive or negative child, and one positive parent paired with one negative parent can also produce either result. The only combination that guarantees an Rh-negative child is two Rh-negative parents, so if you’re A+, at least one of your parents carries the Rh-positive gene.
The Blood Type Diet Has No Evidence
You may have come across claims that people with type A blood should eat a vegetarian or near-vegetarian diet to match their biology. This idea, popularized in the late 1990s, suggests that each blood type evolved alongside different dietary patterns and that eating for your type prevents disease. A systematic review published in The American Journal of Clinical Nutrition searched established medical and scientific databases and found zero studies supporting health benefits from blood-type-based diets. No clinical evidence exists to validate the concept for any blood type, including A. Eating patterns that emphasize vegetables, whole grains, and lean protein benefit everyone regardless of whether their red blood cells carry the A antigen, the B antigen, both, or neither.