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
Hcg can be estimated earliest by : 
Select and explain. 
A. Radioimmunoassay, B. ELISA., C. Radioreceptor assay, D. Bloassay
A: Radioimmunoassay
Answer: A: Radioimmunoassay 
Explanation: Radioimmunoassay is more sensitive and can detect ss subunit of hCG up to 0.002 IU/ml in the serum. It can detect pregnancy as early as 8-9 days after ovulation. Reference:DC Dutta's Textbook of obstetrics,8th edition,page no:76<\p>