How far along do you have to be to find out if you are preg. by taking a blood test?

A blood test will show if you are pregnant or not 7 days following conception.

A home pregnancy test can be used 19 days after the day you think you became pregnant.

Not far at all. I'd say within a day or two of conception. I'd recommend that you wait a while, though, because false negatives are really disappointing.

I didn't find out I was pregnant for sure until I was over a week late. In the meantime, I had lots of false negatives and possibly sort-of positives. In hindsight, I probably would have been much better off without the emotional roller coaster.

They can get pregnancy hormone anytime after conception through blood. If the levels of HCG are greater than 2 then they schedule you to have more blood drawn in 48 hours. If the levels are rising then they consider you positively pregnant and may like to repeat the blood work in another 48 hours.

The blood tests are just as reliable as the home tests. I had a blood test b/c I just knew I was pregnant and it was negative. The very next morning I took another home test and it was positive. Don't waste your money on a blood test.