Lu^a/Lu^b typing. (A) Strategy of the PCR-RFLP. Primers Lu91 and Lu92 were designed to amplify an 81-bp LU gene fragment that encompasses the single base substitution (A229G) identified between the Lu^a and the Lu^b alleles and that correlates with an allele-specific Aci I restriction site. (B) Typical results of the PCR-RFLP assay. DNA from donors with the indicated Lu phenotypes was used in the PCR-RFLP assay. The sizes of the digested fragments are indicated on both sides.