I had a medical abortion 6 weeks ago , could a blood pregnant test still say positive?

Yes: It is vitally important to do weekly blood pregnancy tests until the value goes to non pregnant, usually 0-5 in most labs. If it does not, there is a possibility of an abnormal pregnancy known as a "molar pregnancy", either complete or partial. A value that does not go to 0 may also indicate incomplete emptying of your uterus. In any case at some point a d and c may be needed to clarify the issue.