I'm sorry no one has responded to your post, I'm sure it's because they do not know the exact answer. And well, I'm sorry to say, I don't either, however, I did find this site on HPT sensitivity and it list Dollar General and Family Dollar Tests as 50, but does not say anything about Dollar Tree. Maybe this will help a little .
http://www.fertilityplus.org/faq/hpt.html
~Lisa O~