When you go to the GP it is as simple as knowing you are Vegan... not looking at them like "am I doing the wrong thing here"... ... then you shouldn't hear anything about it.
If you are going to the Nutrition then you don't need to bother asking anything about Veganism to your GP, like "what should I eat to get sufficient nutrients" to them is like "what do I eat to make up for meat lol" ,,, they aren't going to know really. Maybe the odd GP might have a few bits of advice.
But... you are just going "for a blood check-up", mainly for the simple fe studies and B12, but also if they are a good GP they will know a few other good tests to cover all bases from immune system function, live, kidneys and indicators for virsuses (really just immune system function).
I know a good one in Adelaide to go to, but that might not help
Just say you are looking for a thorough range of tests and if you have any particular concerns it is a good chance to ask from referrals and specialised tests to be added to this. They charge a standard fee, so get your moneys worth. Also maybe see if they can mail you the results for later reference or get a copy some how.. after.. or ask the GP to let you know if they are fine so you don't have to do what I did... go in to hear "all good, seeya"..BAM 80$~! Well tbh a year ago I think... when I wasn't Vegan.. or 1 1/2.. I got a letter sent to me saying "follow up check for thyroid needed"... so I guess they.. if you make them your new GP that has all your records etc... will let you know if you need another appointment, but don't make one by default, waste of money.
haha. but anyway.. don't be nervous, you aren't getting a test to prove anything, but reassurances and your results don't prove Veganism or not, they are for your information only to aid your unique ability to learn (some people lack this).. so you are just seeing whether you have left anything out of your diet really... I think with a dietitian you'd best spend some time just talking about when to eat.. not what.. because the net is full of great ideas.
Also there are some Forums where you can raise issues and professionals who are voluntary members really, give lots of nice advice and input.
Anywhoo, have fun.. I find blood test results fun. Even if they aren't perfect. People trash their bodies, you should be nervous about going to a GP when you actually care about yours... they probably see some useless patients.
~ p.s.~
So in summary... just be open with them. You are there because you were Vego but you're Vegan now and need some tests to help you in future to benefit that transition / a future reference for maintaining your positive diet.
Positivity being a personal state of mind, they can't really argue it being positive or negative when it is your choice and you're the one whose mind will feel rewarded or burdened, they can't dictate that
It should never be a debate and if it is you're making them defensive for a reason, so just be open and seeking knowledge and they should be open and sharing. Don't contest what they say directly and don't make it a debate, you should look for perspective not right and wrong.