Hh blood group

The Hh blood group system is defined by the H antigen, a precursor required to form A and B antigens. People with the rare Bombay phenotype lack H antigen and can produce anti-H antibodies.

Connect

H antigen: A fucosylated carbohydrate on red blood cells that serves as the precursor for A and B antigens. It is the defining antigen of the Hh system and the substrate modified by ABO enzymes.
Bombay phenotype: A rare phenotype in which red blood cells lack H antigen and the serum commonly contains anti-H. It is the best-known Hh phenotype and prevents ordinary ABO antigen expression.
Transfusion medicine: The clinical practice of collecting, testing, and transfusing blood and blood components. H antigen status can determine whether a donor unit is safe for a recipient.
Oligosaccharide: A carbohydrate made of a short chain of linked sugar molecules. H antigen is a specific oligosaccharide displayed on cell-surface molecules.
ABO blood group system: A blood group system determined by carbohydrate antigens A and B on red blood cells. A and B antigens are formed by modifying H antigen.
Para-Bombay phenotype: A rare phenotype with absent or very weak red-cell H antigen and variable expression of H substances in secretions. It contrasts with the classic Bombay phenotype through residual or secreted H expression.
Anti-H antibody: An antibody directed against the H antigen, often present in people with the Bombay phenotype. It can react with nearly all ordinary donor red cells, including type O.
Fucose: A deoxy sugar found in human glycans and incorporated into the H antigen. Fucose is the terminal sugar added when H antigen is formed.
FUT1: A gene encoding an enzyme that produces H antigen on red blood cells. FUT1 activity creates the red-cell H antigen that the system classifies.
ABO blood type O: An ABO phenotype whose red cells retain unmodified H antigen because A or B transferase activity is absent. Type O red cells usually display more H antigen than A or B red cells.