The Kleihauer Betke test for detecting foetal erythrocytes is based on the fact that: (A) Adult erythrocytes are larger than those of foetus, (B) HbA has higher oxygen affinity than HbF, (C) HbF is more resistant acid elution than HbA, (D) HbA takes up erythrosin stain less than HbF
Answer is C. 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.