I think they have 2 types of blood tests ?? one where the numbers are given specifically and the other where it just gives you a yes/no answer...

When we first found out we were pregnant it was very early days and i had a blood test and my levels came back at 22, the doctor told me what yours said, if i remember rightly it has to be over 25 for a definate, i worried for the next week as i waited for the next blood test results to check to find out that the levels had risen and all was fine, i was just very early pregnant.

Which by the looks of it you are as well. So Congratulations to you