Human chorionic gonadotropin can be measured from the urine or blood serum. HCG measurements may be quantitative (measuring the amount of hCG) or qualitative (indicating if hCG is present or not).
Pregnancy can cause a positive hCG test as hCG is secreted once the fertilized egg implants into the uterine lining. HCG levels continue to rise until the 14th week of pregnancy.
Sometimes hCG is given in an injection to women being treated for infertility. This injection of hCG can cause a positive result on blood and urine tests if it has been seven to 14 days after the injection.
Reproductive tumors may sometimes produce hCG, as in the case of hydatiform moles or choriocarcinomas. Germ cell cancers may also cause a positive hCG test.
A pregnancy that implants outside of the uterus is an ectopic pregnancy. A study performed in the Netherlands in 1990 by D.J. Tinga, J.J. van Lier and H.W. de Bruijn suggests these pregnancies produce hCG that could test positive in urine or blood, but generally at a slower rate than a viable pregnancy.
While going through a miscarriage hCG tests will remain positive. According to the American Pregnancy Association, hCG may test positive for a month or more after a miscarriage.