Quoted from BTD FAQ Some people on other internet boards claim that blood testing for secretor status is superior to the saliva test. Is that true?
http://www.dadamo.com/errata/smartfaq.cgi?answer=1075206948

Dr. D'Adamo had this to say about differences in secretor testing: "Having done 5000 Lewis typing tests in the clinic over the last 15 years, and about 400 salivary inhibition studies, I can safely say that saliva testing is more accurate than blood. The reason being that the agglutinations that are used to determine Lewis types are very delicate (weak antibody reaction) and can easily be misinterpreted, unlike ABO which makes a big glop that you cannot miss (strong antibody). I've even seen conflicting results from two different MedPath labs, especially if the staff is not trained well enough." The subject is discussed in more depth in one of the Science Knowledge Base Entries.

Quoted from BTD FAQ - Some people on other internet boards claim that blood testing for secretor status is superior to the saliva test. Is that true?
http://www.dadamo.com/errata/smartfaq.cgi?answer=1075206948

Dr. D'Adamo had this to say about differences in secretor testing: "Having done 5000 Lewis typing tests in the clinic over the last 15 years, and about 400 salivary inhibition studies, I can safely say that saliva testing is more accurate than blood. The reason being that the agglutinations that are used to determine Lewis types are very delicate (weak antibody reaction) and can easily be misinterpreted, unlike ABO which makes a big glop that you cannot miss (strong antibody). I've even seen conflicting results from two different MedPath labs, especially if the staff is not trained well enough." The subject is discussed in more depth in one of the Science Knowledge Base Entries.

Quoted from Don

If your mother and father are both non-secretors, then you have to be a non-secretor.

Quoted from Lloyd

Of course, if you might have been adopted or switched in the hospital or something.....