It is possible to have positive urine
and negative blood.
The home urine tests are pretty sensitive- namely they don't miss much. They are looking for a HCG of 20 miu/ml and the blood test is looking for a level of 25 miu/ml. So if you were super early and your level was 22 miu/ml your urine would be positive and the blood negative. Repeat the blood in 1 week and then see, good chance its + !