How soon can you take a hCG blood test. And how accurate is it. Can I take only one or is more needed.

HCG test. A blood, or urine, HCG test should be positive about 10 days after conception - even before you've missed a period. Both will tell you if you are pregnant. If you are concerned about miscarriage, the blood quantitative HCG test will help. This test will need to be done and then repeated again in 2-3 days to make sure the HCG is rising normally.