It's rather a long story, so to keep it brief, I had a B12 level of 127 (reference range 180-900) last year, was very symptomatic, and have spent 12 months battling with GPs and haematologists to get treated properly.
My last B12 injection was 29th February 2016 and I am due some blood tests on 7th April (which will be 5 and a half weeks since that last injection). My GP has agreed not to test my B12 levels as we both know they will be high (and I didn't want to give him any reason to stop injections altogether!). But I have asked him to do full blood count, iron levels (as I have suffered from iron deficiency anaemia in the past), potassium, calcium, liver work, thyroid and folate, as some of my symptoms have been returning and I want to rule out any other issues before tackling the "can I have more frequent B12 injections" battle.
Other than taking vitamin supplements, what are the other factors that can affect blood tests? For example, do iron levels vary throughout the month (for women!)? Can what you eat the days before a blood test affect any of the results? Having a glass of wine the night before? Does the time of day affect anything? Fasting? Are all these levels relatively stable or can they fluctuate significantly? etc ...
I obviously want to do my best to make sure the blood test is as accurate as I can, and don't want to inadvertently do anything that skews it!
Thanks for any advice