Minimum level of Beta Hcg detected by radioimmunoassay is :

* Radioimmunoassay (RIA) -- It using I125 ido hCG antibodies. It is more sensitive and can detect b subunit of hCG upto 0.002 IU/mL in the serum. It can detect pregnancy as early as 8-9 days after ovulation (day of blastocyst implantation). Radio receptor assay gives highest sensitivity of 0.001 IU/mL in the serum. RIAs are quantitative, so can be used for determining the doubling time of hCG (ectopic pregnancy monitoring). RIAs require 3-4 hours to perform. Reference : D C dutta's Textbook of Obstetrics 7th edition page no 67