The Kleihauer Betke test for detecting foetal erythrocytes is based on the fact that
The most commonly used quantitative test for fetal red cells in the maternal circulation is the acid elution or Kleihauer Betke test. Fetal erythrocytes contain HbF, which is more resistant to acid elution than HbA.
Adult erythrocytes are larger than those of foetus
HbA has higher oxygen affinity than HbF
HbF is more resistant acid elution than HbA
HbA takes up erythrosin stain less than HbF
Intra Uterine Growth Restriction, Intrapaum and Antepaum Fetal Surviellance