Has any of you ever used a OPK as a pregnancy test?

I read that an opk can detect pregnancy before a hpt can because it detects a lower amount of HCG. I bought some dollar store hpt's today. Last night I took a opk and it was negative, this morning I took a opk and a hpt, the hpt was negative and the opk was negative but it had the slightest line. So I just took another opk and I got the blinking face and the line was a little darker then this morning. So now I'm just curious... I'm will take another hpt in the morning and for the next few days... The bottom one is the one that was positive, the line is thicker but you can't tell that good in this photo.