Blood Test Accuracy

I have heard that blood test can pick up HCG by 10dpo...baby dust!

If you are sure about ur DPO confirmed by an OPK or U/S then by 11 DPO u should be able to detect HCG in the blood. If they did a qualitative blood test as opposed to quantitative, then the result may be -ve based in the standard set by the lab to be classified as 'pregnant'