How to Use the Blood Type Compatibility Tool

Select your blood type — choose from all 8 ABO/Rh combinations: O-, O+, A-, A+, B-, B+, AB-, AB+.
Read donation compatibility — which blood types can receive your blood (who you can donate to).
Read reception compatibility — which blood types you can receive blood from.
Review the compatibility facts — universal donor and recipient information, and blood type frequency statistics.
Share or save — copy the result for medical records or emergency information cards.

🩸 Know your blood type: Your blood type should be on your medical records. If unknown, your doctor can order a simple blood test. In an emergency, O- blood (universal donor) is given when type is unknown — but knowing your type allows more precise matching and preserves the limited O- supply for those who truly need it.

Understanding Blood Types

🧬 The ABO System

Blood type is determined by antigens (proteins) on red blood cell surfaces. Type A: A antigens + B antibodies. Type B: B antigens + A antibodies. Type AB: both antigens, no antibodies. Type O: no antigens, both antibodies. Transfusing incompatible blood triggers immune attack — potentially fatal.

🔴 The Rh Factor

The Rh factor (Rh antigen) creates the + or − designation. Rh positive (Rh+): Rh antigen present on red blood cells. Rh negative (Rh-): no Rh antigen. Rh- individuals can receive Rh- blood only. Rh+ individuals can receive both Rh+ and Rh- blood.

🌍 Blood Type Frequency

O+: ~38% (most common). A+: ~34%. B+: ~9%. AB+: ~3.4%. O-: ~7% (universal donor, critically important). A-: ~6%. B-: ~2%. AB-: ~1% (rarest common type). Frequencies vary significantly by ethnicity and region.

⚡ Universal Donors and Recipients

O- red blood cells: universal donor for emergency transfusions (no A, B, or Rh antigens to react with). AB+ plasma: universal donor for plasma transfusions. AB+: universal recipient for red blood cells (has A, B, and Rh antigens — no antibodies to react). O-: most restricted recipient (can only receive O-).

🤰 Rh and Pregnancy

If an Rh- mother carries an Rh+ baby (inherited from father), the mother may develop Rh antibodies after first exposure. Subsequent Rh+ pregnancies risk haemolytic disease of the newborn. Rh immunoglobulin (RhIg/RhoGAM) injections at 28 weeks and after delivery prevent this sensitisation.

🏥 Blood Type Beyond Transfusion

Blood type is associated (weakly) with risk profiles for certain diseases. Type O: lower risk of heart disease, higher risk of stomach ulcers. Type A: higher risk of stomach cancer. These associations are weak and do not justify medical decisions. 'Blood type diets' promoting different diets for different blood types have no scientific support.

Blood Donation and Compatibility

Why blood donation matters

Blood cannot be manufactured — it must come from donors. Every 2 seconds, someone in the US needs blood. One donation can save up to 3 lives (red cells, platelets, and plasma are separated and used independently). O- blood is in constant critical shortage — needed for emergency situations and newborn transfusions. Regular donations (every 56 days for whole blood) maintain supply for surgical patients, cancer treatment, trauma victims, and people with blood disorders.

Donation eligibility basics

General requirements: age 17+ (16 with parental consent in some states), weight 110+ lbs, good general health, no certain medications or recent tattoos/piercings, no recent travel to certain regions. HIV, hepatitis, and certain other conditions may disqualify donation. Visit your national blood service website for complete eligibility criteria — many temporary disqualifications exist that donors are unaware of.

Plasma and platelet donation

Beyond whole blood donation, plasma and platelet donations are often in greater need. Plasma can be donated every 28 days (whole blood every 56 days). AB plasma is universal — AB blood type donors are uniquely valuable for plasma. Platelet donation uses apheresis technology that returns red cells and plasma to the donor — taking only platelets, which are critical for cancer patients and surgery. Platelet donors can donate up to 24 times per year.

🩸 Blood donation facts: A donation takes 8–10 minutes. You have about 10 pints of blood — you donate 1 pint. Your body replenishes plasma within 24 hours. Red blood cells take 4–6 weeks to fully regenerate. One donation can save up to 3 lives. You can donate whole blood every 56 days. Finding a donation centre: visit RedCrossBlood.org (US) or your national blood service website.

Frequently Asked Questions

What are the 8 blood types?

The ABO blood group system has 4 types: A, B, AB, O. The Rh factor adds + or −, giving 8 types: A+, A−, B+, B−, AB+, AB−, O+, O−. Your type is determined by antigens on red blood cells and antibodies in plasma.

Who is the universal donor?

O− (O negative) is the universal donor for red blood cells — anyone can receive O− blood in emergencies. O+ can donate to any positive blood type (A+, B+, AB+, O+). O blood types are most needed by blood banks.

Who is the universal recipient?

AB+ (AB positive) is the universal recipient — they can receive blood from all 8 blood types. AB blood types can also receive plasma from any donor. AB+ is the rarest common blood type (~3.4% of population).