Quick progesterone blood draw question.

nena • I wouldn`t change a thing. TTC baby #1

So my doctor would like for me to go in on CD 21 (August 8)to get my progesterone levels; but I am planning on going on a mini vacay that week.

I guess my question is can I get my blood drawn August 3 on CD 16 or should I wait and get it done on CD 21.

It may sound like a dumb question but i would really love to hear your opinions.