Secretor status refers to the presence or absence of water-soluble ABO blood group antigens in a person's bodily fluids, such as saliva, tears, breast milk, urine, and semen.
[note 1] The Se gene, which encodes the enzyme α-2-L-fucosyltransferase, controls the formation of H antigen in bodily secretions.
In people with the secretor genotype, the enzyme converts a precursor substance found in body fluids to the H antigen, which is then modified by the glycosyltransferases encoded by the ABO gene to produce the antigens corresponding to the person's ABO blood type.
In individuals who are positive for Le, the blood type is determined by the person's secretor status.
[note 2][1]: 178–81 [3]: 196 Noroviruses bind to secreted blood group antigens on the mucosa of the digestive tract.
In the serologic method, the person's saliva is boiled, then added to reagents containing antibodies against the A, B, and H antigens.