The Lewis test is for secretor/non-secretor status.
The results can be either:
- Lea+ Leb- (non-secretor),
- Lea- Leb+ (secretor), or
- Lea- Leb- (Lewis negative)
About 5% of people are Lewis negative, these people can't find their secretor status with the Lewis test, they should use a saliva test or DNA test.
Secretor status is used for following the blood group diet at an advanced level, as in the book Live Right 4 Your Type, or to calculate your GenoType in The GenoType Diet: Change Your Genetic Destiny.