What to ask GP for in a blood test?

[sip1]

It was a few months back when I had my last blood test, October in fact! Where I found I was/am low in ferritin and b12. I'm fairly sure it's too soon to know if these have improved yet, but since I'm having it done anyway, how long should I leave taking iron and b12? Also, should I ask to get anything else checked (my thyroid meds have not long been increased so that prob won't be a reliable number either yet). I did my own vit d, so won't need that. My fatigue is ridiculous at the moment...

[SeasideSusie Remembering]

sip1 You should leave off iron for 5-7 days. B12 has to be left off for about 5 months if you want a baseline to see how much you are holding on to. Testing whilst supplementing ring just tells you that you are supplementing, but it's still quite useful because you can see if you're taking enough.

You need folate testing as that works with B12.

You could always ask for zinc, as that helps T4 to T3 conversion, not sure if you'll get it done though, also selenium.

Have you had Thyroid Antibodies tested?

[sip1 in reply to SeasideSusie]

Yes I did a while ago my appointment is Tues so will stop taking iron today. Thank you x

[sip1 in reply to SeasideSusie]

Shall i just not take my daily b12 on the day of the test?

[bluebug in reply to sip1]

Won't make much of a difference.

The only thing I've been told is not to take it for 48 hours so your result isn't so over range it scares the GP.

Edited to add: I read the NICE guidelines and they suggest having a full blood count to monitor vitamin B12 levels as those who are very low levels should have large red blood cells. However if you have low iron specifically haemoglobin then your red blood cells will look normal, as low iron causes smaller red blood cells.