B-

B- Blood Type

Rare - 1.5% of US donors

B-negative blood carries the B antigen but lacks the Rh-D antigen. It is the second rarest of the 8 major blood types, found in approximately 1.5% of US donors. B-negative donors are especially valuable: they can donate to B-positive, B-negative, AB-positive, and AB-negative recipients. Because B-negative lacks Rh-D, it is also safe for Rh-negative B and AB patients.

Can donate red cells to:

B+B-AB+AB-

4 compatible types

Can receive red cells from:

B-O-

2 compatible types

What Is B- Blood?

Antigens present

B antigen only (no A, no Rh-D)

Antibodies produced

Anti-A (anti-D only if sensitised)

Antigens are proteins on the surface of red blood cells. The ABO antibodies (anti-A and anti-B) are naturally occurring - present from infancy against whichever A or B antigen you lack. The Rh anti-D antibody is different: Rh-negative people do not carry it from birth and only form it after exposure to Rh-positive blood through transfusion or pregnancy (sensitisation), which is why anti-D immunoglobulin is given to prevent it. When incompatible blood is transfused, antibodies bind to foreign antigens and trigger a haemolytic reaction.

Interactive Compatibility Tool

Select your blood type:

B-Rare - 1.5% of US donors

Can donate red cells to:

B+B-AB+AB-

4 compatible types

Can receive red cells from:

B-O-

2 compatible types

Full B- guide

How Rare Is B-?

Population	Frequency
US blood donors (Red Cross estimate)	1.5%
Global population (estimate)	1.7%

B-negative is found in approximately 1.5% of US donors and about 1.7% of the world population. It is one of the rarest of the 8 major types. Only AB-negative (0.6%) is rarer. B-negative is relatively more common in South Asian populations than in Europe or North America, but even there it remains uncommon compared to B-positive. Blood banks closely monitor B-negative stocks.

Clinical Notes for B-

B-negative individuals share B-type ABO characteristics. Being Rh-negative has no known direct health implications in everyday life - it only becomes medically relevant in transfusion and pregnancy contexts. B-negative donors are highly valuable and should donate as regularly as possible. Whole blood donation is available every 56 days; platelets every 7 days. Because B-negative is rare, matching compatible blood quickly in an emergency can be challenging, which reinforces the importance of regular donation from B-negative individuals.

Note: Associations between blood type and disease risk are from observational studies and are not deterministic. They do not change your clinical management. Cite any specific associations with your clinician.

Pregnancy Implications for B-

B-negative mothers are Rh-negative. If the father is Rh-positive, your baby may be Rh-positive, triggering the risk of Rh incompatibility. Anti-D immunoglobulin prophylaxis (RhoGAM) is offered to all Rh-negative mothers at around 28 weeks and within 72 hours of delivery. This treatment is highly effective at preventing sensitisation. If you are B-negative and planning a pregnancy, inform your obstetrician of your blood type early. Additional anti-D doses may be needed after any procedure or incident that could cause fetal-maternal bleeding (amniocentesis, chorionic villus sampling, or significant abdominal trauma).

Full Rh factor pregnancy guide +

Organ Transplant Compatibility for B-

B-negative organ donors can give organs to B+, B-, AB+, and AB- recipients. As a B-negative recipient, you can only receive organs from B-negative or O-negative donors - a significantly restricted pool. This is an important consideration for patients on transplant waiting lists: B-negative patients may face longer wait times due to fewer compatible donors. Living donor paired kidney exchange programs are particularly relevant for B-negative patients who have an incompatible willing donor.

ABO compatibility for organ transplant follows the same rules as transfusion - B- can donate organs to: B+, B-, AB+, AB-. However, HLA tissue matching and crossmatch testing are also required, and sensitisation from prior transfusions or pregnancies can restrict compatibility further.

Full organ transplant guide +

Plasma Donation for B-

B-type plasma contains anti-A antibodies and can be given to B or O recipients. The Rh factor does not affect plasma compatibility. If you are B-negative, your most impactful donations are red cell donations (either whole blood or double red cells), not plasma.

Note: Plasma compatibility rules are the inverse of red-cell rules because plasma carries antibodies, not antigens. AB plasma is the universal plasma donor.

Plasma compatibility chart +

Frequently Asked Questions about B-

Who can B-negative donate blood to?

B-negative can donate red cells to B+, B-, AB+, and AB-. These four types can all accept B antigens without a reaction, and because B-negative lacks Rh-D, it is safe for both Rh-positive and Rh-negative recipients within the compatible ABO types.

Who can B-negative receive blood from?

B-negative can only receive red cells from B-negative or O-negative donors. B-negative people produce naturally-occurring anti-A antibodies (ruling out A and AB types), and being Rh-negative they would form anti-D antibodies if given Rh-positive blood, so all Rh-positive types are avoided.

How rare is B-negative blood?

B-negative accounts for approximately 1.5% of US donors - only 15 in every 1,000 donors. Only AB-negative is rarer among the 8 major types. If you are B-negative, you are in a small group of highly valuable donors, and regular donation makes a real difference.

What if a B-negative patient needs an emergency transfusion and B-negative is unavailable?

In an emergency, O-negative (the universal donor) would be used. Hospitals maintain O-negative emergency reserves for exactly this scenario. If a B-negative patient can wait for blood typing, B-negative or O-negative would be the correct match. In critical shortages, B-positive might be used with careful risk assessment, though this risks Rh sensitisation in patients who may need future transfusions.

Can B-negative and A-negative parents have a B-negative child?

It is possible but depends on the specific genotypes. An A-negative parent (with at least one O allele) and a B-negative parent can have a child who inherits the B allele and the O allele, resulting in BO genotype (B-type, negative). The exact probability depends on whether each parent is homozygous or heterozygous for the A or B allele.

Related Blood Types

B+O-AB-O+