This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: General obstetrics, Subject name: Gynaecology & Obstetrics
Which test differentiates maternal and fetal blood cell? 
Select and explain. 
A. APT test, B. Kleihauer test, C. Bubble test, D. Lilly's test
A: APT test
Answer: A: APT test 
Explanation: Apt test can be performed to confirm a fetal bleed and there by vasa prae.Apt test is based on the principle that fetal haemoglobin is more resistant to alkali denaturation .Therefore when water and blood are mixed with sodium hydroxide it remains pink for longer if fetal in origin (refer pgno:138 sheila textbook of obstetrics 2nd edition)