I was advised not to use Antech for progesterone test, but to use Pheonix Labs as they give a better result. I can't speak to Idexx, that is not an option for me.
I was only using Antech because it was the only thing available in my area at the time, until I learned I could drive the sample 30 miles myself to be collected at a clinic that used Pheonix. Now, Pheonix is available here, so I hope that continues.