Hi, Five Years Ago I Was Diagnosed With Celiac Disease,

Hi, five years ago i was diagnosed with celiac disease, but it wasn't documented. I have been gluten free for 5 years and my health has improved. However, I need my celiac disease documented so i can get proper gluten free accomadations (food and meds) for an upcoming surgery. I took arecent blood test. It came up negative since i have been gluten free for 5 years. How much gluten and over how much time do i need to eat it to get a positive blood test for documentation?