Secretors/Non-Secretors and Blood Group

[pekeboo]

I am trying to understand the difference between secretors and non-secretors. I have read that secretors pass antigens into secretions such as saliva which identify blood group. If this is the case why are blood grouping tests not conducted simply with a sample of saliva rather than blood? Can someone explain?

[biohazard]

For common ABO blood typing, the antigens on the surface of erythrocytes are determined, rather than antibodies circulating in the blood. I think one could rather easily determine someone's blood type even from saliva, since minute amounts of red blood cells (and antibodies) are found in the saliva. However, for that one would need very precise (=expensive) equipment and reagents, and probably quite a lot of saliva as well. Not to mention measuring anti-A or B type antibodies, which would require pretty expensive and complicated methods to detect - unless someone secretes a lot of blood type specific antibodies, of which at least I am not aware of.

To the contrary, blood is easy to achieve in small or large quantities, and more importantly the stuff you want to measure is best found there. Furthermore, ABO blood typing can be carried out extremely easily from whole blood (even on your bench top with a blood lancet and two reagent bottles ). And if you want to take the typing further and search for rarer blood type antigens or circulating antibodies, then you need enough of red cells (or plasma for antibodies) to carry out all these tests, and again, mere saliva does not provide enough of cells or antibodies. So, there is no real reason to try to measure blood types from saliva that I can think of. Well, someone who is very afraid of needles might disagree, but still...