Full blood count

[RosaDiazepam]

What will this tell the GP? Will they be able to tell vitamin/mineral deficiencies?

It will tell them if you are anaemic or not and if you are give a hint as to what sort of anaemia sometimes although not always. It also tells you if you have the right number of platelets which help your blood clot - this is very rarely why you do the test or relevant, and the right number of white blood cells - usually only relevant if you have an infection but there are other reasons.

From your question, although you don't say your symptoms, I'm guessing your GP is interested if you are anaemic.

Apart from iron studies and Vit D levels, both of which you would only test for if symptoms suggested you should, it's exceptionally rare to measure any other sort of mineral or vitamin deficiency.