Different brands may have varying degrees of sensitivity. For example, one brand requires a urine hCG level of 20 or 25 mIU/cc to be positive, but another brand requires 50 mIU/cc to be positive. That might explain why one test results in a positive result while the other results in a negative result. You should try again using a different sample of urine if one sample is not conclusive. It is unlikely that you will need to repeat a urine test. Most brands can detect a level as low as 5 mIU/cc. But if you are unsure then it is best to follow your doctor's advice. Sometimes women with very high levels of hCG do not show any signs of pregnancy until well into their second trimester. If you are concerned about possible exposure to hCG from a previous pregnancy or a cancer diagnosis, then it is advisable to have regular blood tests throughout your pregnancy.