Blood tests on a random cycle day?

[MelonZebra]

I went to my GP as I've had very light periods and worried about conceiving. She's sent me for blood tests for prolactin, LH, TSH, oestradiol etc but I thought some of these were day 3 / day 21 (or 7 dpo) specific? As it happens, I am on CD21 but only 3 dpo. She didn't ask when my last period was just how long in general my cycles have been and how long I bleed for. Is this even going to tell them anything if I'm on the wrong cycle day?

I may be completely wrong as I’m not an expert but I think it’s CD3 or 7dpo… CD21 is based on a ‘typical’ ovulation on CD14 - which would equate to 7dpo. Think they go for CD21 for those who don’t have regular cycles or don’t know when/if they ovulate. I’d see if you can go when you’re actually 7dpo.

My last cycle I was 7dpo on CD20 so had the bloods on CD20

Progesterone is the one that needs to be tested 7dpo (which is to check if you have ovulated) - the others can be at different times of the month and he checked against what the average level will be at that stage in your cycle.

Usually though these are done on day 3 to check base levels for estrogen, FSH and LH. If you can book these for day 3 it'll be most useful.

Sorry yes I should have clarified I know CD21 is based off "typical". That was poorly worded on my part in my OP sorry and CD21 wouldn't work for me most months.

I did ask the phlebotomist today and she seemed to think mine didn't need to be CD3 or 7 dpo specific. So I guess I'll see what happens and then go from there. Problem is they don't actually know what cycle day I'm on as they didn't ask so not sure how they'll average it.