Hi there - Just in case you've somehow accidentally contaminated an arm, maybe ask them to take the blood from your other arm if possible?
Try to get it taken when you are on your period, because that's when the estrogen from your own body will be lowest and will give you the clearest picture of what you're getting from HRT. For eg, maybe you had just ovulated last time, which can cause estrogen to spike up to 1300pmol - that is the normal reference range for ovulation. And then around your period, maybe you are down very low... It's the lows you want to catch so you can buffer them out with HRT.