Why will a test be still positive afer a DnC?

The pregnancy hormones are still in your system.
Most women can expect their levels to return to a non-pregnant range about 4 - 6 weeks after a pregnancy loss has occurred. This can differentiate by how the loss occurred (spontaneous miscarriage, D & C procedure, abortion, natural delivery) and how high the levels were at the time of the loss. Health care providers usually will continue to test hCG levels after a pregnancy loss to ensure they return back to <5.0