Fetal genotyping for the K (Kell) and Rh C, c, and E blood groups on cell-free fetal DNA in maternal plasma.
BACKGROUND
When a pregnant woman has an antibody with the potential to cause hemolytic disease of the fetus and newborn, it is beneficial to determine whether her fetus has the corresponding antigen to assess risk. In many countries this is now done routinely for RhD, by testing cell-free fetal DNA in the maternal plasma. Similar tests for K, C, c, and E are reported.


METHODS
Real-time quantitative polymerase chain reaction incorporating an allele-specific primer was developed for detecting the K allele of KEL and the C, c, and E alleles of RHCE. These methods were used to test DNA isolated from plasma of pregnant women with antibodies to K, C, c, or E. Accuracy of the tests was determined by comparing results with serologic tests performed on cord red blood cells (RBCs) after delivery or by molecular genotyping on DNA obtained from fetal cells.


RESULTS
The K test incorporated an allele-specific primer with two locked nucleic acids and a mismatch. In 70 tests, including 27 K+ fetuses, only one false-negative and no false-positive results were obtained. The C, c, and E tests, performed on 13, 44, and 46 samples, respectively, gave rise to no false results.


CONCLUSIONS
Reliable methods have been developed for predicting fetal K, C, c, and E phenotypes, by testing fetal DNA in the plasma samples of pregnant women whose RBCs lack the corresponding antigens. These methods are now being used routinely in a diagnostic service in the United Kingdom.
Finning
Kirstin
K
International Blood Group Reference Laboratory, NHSBT, Bristol, UK.
Martin
Peter
P
Summers
Joanna
J
Daniels
Geoff
G
D000328:Adult; D000483:Alleles; D004247:DNA / Q000097:blood*; D017931:DNA Primers; D003951:Diagnostic Errors; D005260:Female; D005333:Fetus; D005838:Genotype; D006801:Humans; D007626:Kell Blood-Group System / Q000235:genetics*; D009035:Mothers; D016133:Polymerase Chain Reaction / Q000592:standards; D011247:Pregnancy; D012204:Rh-Hr Blood-Group System / Q000235:genetics*; D012680:Sensitivity and Specificity
D017931:DNA Primers; D007626:Kell Blood-Group System; C066468:RHCE protein, human; D012204:Rh-Hr Blood-Group System; D004247:DNA