This does not make sense...

So on Wednesday I got a faint positive on an Internet cheapie that detects 25miu and also a faint positive on a first response. That evening I had my blood drawn and was told my levels were 6 hcg. I thought it was a miscarriage but hard to tell because I was 3 days before my missed period. However, how would the tests have detected 6miu in the first place? I took another Internet cheapie this morning and it showed a darker line, so I am beyond confused.