What dictates how much hcg is present in the blood of a non pregnant woman?

It is not normal: If you are not pregnant, there should be no HCG in the blood. Certain tumors of the ovary, lung, stomach and liver can secrete hcg.

Should be none: There should be no HCG in the blood of a non pregnant woman, with very few exceptions: 1) a woman with persistent gestational trophoblastic disease / choriocarcinoma 2) a woman who recently was pregnant or miscarried (whose level of HCG will be falling) 3) a woman who is taking exogenous HCG (ie HCG diet, injections for fertility).

Usually none.: Agree with other answers. Unusual but some pituitaries actually manufacture low levels of hcg. More commonly seen in menopause. This is relatively rare.