A celiac disease test will not be accurate, if you have been on a gluten-free diet for more than a few months. If you are in this situation, there are a few options to consider.
Find out if you have celiac disease.
Celiac disease is an auto-immune disease. In genetically susceptible individuals, the body produces auto -antibodies when gluten is eaten. An extremely strict gluten-free diet is needed in celiac disease. If you don’t have celiac disease, but feel better without gluten, the degree of restriction is up to you. I’ve met many clients on a gluten-free that “cheat” occasionally. Unfortunately, this occasional intake of gluten can result in widespread, serious damage to the body, if they have celiac disease. A conclusive celiac diagnosis, helps people take the restriction more seriously.
Additionally, gluten-free foods can be a federal tax deduction, if you have a letter from your medical doctor confirming that you have celiac disease.
Before eliminating gluten, get tested for celiac disease.
This is important for everyone, but even more important if you have:
1) a close relative with celiac disease
2) common symptoms (e.g. anemia, fatigue, etc. see additional symptoms).
3) conditions that commonly overlap with celiac disease (e.g. type 1 diabetes, thyroid disease, etc. see additional conditions).
The diagnosis starts with a blood test to detect the auto-antibodies (tTgG and/or EMA). Your family doctor can order it, or you can purchase home kits, such as: CeliacSure Test. If the auto-antibody test is positive, you will likely be referred to a gastroenterologist for a small intestine biopsy (celiac disease causes the small intestine to flatten).
If you have been on a strict gluten-free diet for more than a few months, the blood test and biopsy may be negative (even if you have celiac disease).
The body starts to heal (stops producing auto-antibodies and the small intestine recovers), when a gluten-free diet is started. If you are on a gluten-free diet and are concerned that you may have celiac disease, you can:
1) Reintroduce gluten into your diet and have the screening test. There is no accepted consensus on how much gluten and for how long you need to include it in your diet. A typical recommendation is to eat two slices of bread (or the equivalent of other gluten containing food) each day for about two months. However, most people that are feeling better on a gluten-free diet, don’t want to reintroduce it.
2) Have a genetic test for HLA DQ2 and DQ8. These genes are necessary for celiac disease. If you do not have either gene, you do not have celiac disease and will not develop it. However, about 30% of the population have one or both of these genes and only 1% has celiac disease, so having the genes does not mean you have celiac disease.
3) Assume you have celiac disease and follow a very strict diet (even excluding foods that may be contaminated with gluten).

Not sure what to eat? I can help you sort through the confusing information and make a meal plan.
My doctor didn’t tell me this before I went on a gluten free diet.
There needs to be more education on this topic for the medical community.