Quick answer
B negative (B−) means red blood cells carry the B antigen but not the RhD antigen. B− red cells can generally be given to B−, B+, AB−, and AB+ recipients, and B− people can generally receive red cells only from B− and O− donors.
What B− means
The B indicates the B antigen on red cells, with anti-A antibodies typically in plasma. The minus sign indicates the RhD antigen is absent.
As an Rh-negative type, B− recipients are generally matched with Rh-negative red cells, limiting compatible donors to B− and O−.
B negative is among the less common blood types in many populations, so blood services often encourage B− donors to give regularly.
| Property | Value |
|---|---|
| ABO group | B |
| Rh (D) status | Negative (RhD antigen absent) |
| Red cell antigens | B |
| Plasma antibodies (typical) | anti-A |
Compatibility summary
General red cell and plasma compatibility for B− under the simplified ABO/Rh model. Real transfusions also depend on antibody screening and crossmatching.
| Product | Can give to | Can receive from |
|---|---|---|
| Red blood cells | B−, B+, AB−, AB+ | O−, B− |
| Plasma (ABO only) | B, O | B, AB |
See the full compatibility chart for all eight types.
Inheritance context
Type B can result from BB or BO genotypes; Rh-negative requires the dd genotype.
A B− child could have Rh-positive parents if both carry a hidden d allele (Dd).
Under the standard model, at least one parent must carry a B allele (type B or AB). A type B child is not expected from two type O parents, or from an A and an O parent, because neither would carry B.
Work through specific parent combinations with the baby blood type calculator, or find which parent types could produce a B− child with the parent calculator.
Limitations
- Blood type can only be confirmed by laboratory testing. Family history, calculators, and self-report are not substitutes.
- Compatibility rules on this page are general educational summaries. Real transfusion decisions also depend on antibody screening, crossmatching, product type, and clinical judgment.
- Rare variants such as the Bombay phenotype, cis-AB, and weak or partial D expression can produce results that differ from the simplified ABO/Rh model.