This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Miscellaneous (Bio-Chemistry), Subject name: Biochemistry
Alkali resistant haemoglobin is - 
Select and explain. 
A. HbA, B. HbA2, C. HbF, D. HbS
C: HbF
Answer: C: HbF 
Explanation: Ans. is 'c' i.e., HbF* Adult haemoglobin is made up of a2b2* Foetal haemoglobin is made up of a2g2* Adult haemoglobin undergoes denaturation in the presence of alkali to form alkaline hematin. Alkaline hematin is insoluble and precipitates.* On the contrary foetal haemoglobin is resistant to alkali denaturation.* This is the basis of estimation of foetal haemoglobin, wherein HbF is quantitated by measuring the hemoglobin concentration before and after denaturation.* It is also the basis of alkali denaturation test or Apt test or Apt - Downey test used to differentiate foetal blood from maternal blood in a new born stool or vomitus.* After treatment with alkali, foetal hemoglobin will appear as a pinkish colour under the microscope while the adult hemoglobin will appear as a yellow-brownish colour.* A positive result is when pink colour is observed and is diagnosed as foetal bleeding.* A negative result is when yellow brownish colour is observed and is diagnosed as the neonatal swallowing of maternal blood.