Noninvasive diagnostics of fetal KEL*01.01 allele from maternal plasma of immunized women using digital PCR protocols

Allo-antibodies produced by K-negative pregnant women against a fetal K antigen from the Kell blood group system may cause hemolytic disease of the fetus and newborn (HDFN). Predicting the fetal K antigen using noninvasive prenatal testing (NIPT) is important for decisions concerning management of pregnancies. Digital and droplet digital PCR techniques permit the detection of fetal single nucleotide variant with a higher specificity and sensitivity than real-time polymerase chain reaction (PCR).

Aim: The aim was to evaluate and compare protocols for fetal KEL*01.01 genotyping using different assays and digital PCR platforms.

Methods: DNA isolated from 59 pregnant women (9-39 weeks of gestation, 49 with anti-K) was tested using home-made and custom-ordered KEL*01.01/KEL*02 assays with Droplet Digital™ and QuantStudio™3D. The results were compared with fetal/neonatal genotypes/phenotypes.

Results: Fetal KEL*01.01 results using all tested protocols were concordant with fetal/neonatal KEL*01.01 genotypes/phenotypes. None of the tested combinations of assays or digital PCR platforms gave false KEL*01.01-negative results, but inconclusive KEL*01.01 reads were observed in all tested protocols. For 36 cases compared using two digital PCR platforms and assays, there were not statistically significant differences in a level of fetal KEL*01.01 fraction (p < .72).

Conclusion: Independent of the applied dPCR and ddPCR platforms and KEL*01.01 assays, prediction of the fetal KEL*01.01 is highly reliable. Before implementation in routine practice further validation of the KEL*01.01 protocol with a larger group of pregnant women should be performed.