I have a seven year old who is slow growing as well. No other symptoms. His blood tests (anti-endomysial ema) came back negative, but we did a 6 month trial on gf and saw and inch of growth. Now I have a negative test and growth on GF. I guess endoscopy is always an option but I hate to put him through that. I currently took him of gf as per docs suggestion and a allowing as much gluten as desired and then we'll retest.
My thoughts....one thought is, why on Earth should you put him back on gluten? I know that your doctor probably thinks that the gluten free diet is torture (like most people who eat a "normal", wheat-filled diet), but you know better! At least I assume you know by now that you can eat just as well on the gluten free diet as before...? If you don't know that, well, let me assure you it's true! :)
Of course your son tested negative on the bloodwork, he's been off gluten for 6 months! He will also be negative on the biopsy right now.
The bloodwork is notoriously inaccurate in young children anyway, and the biopsy is hit or miss at best, even if he had been eating gluten the whole time! Response to the gluten free diet is the best test of all, and your son has responded beautifully already to that one!
If what you are doing is working, why change anything?
I have celiac disease, I tried to feed my family gluten and stay gluten free but I was constantly being cross-contaminated by crumbs. So I put the entire family on the gluten free diet and, lo and behold, my son's skin conditions improved and so did my daughter's (keratosis pilaris and eczema). My daughter has also been diagnosed as Failure to Thrive; at 2 1/2 years of age she wore clothes for a 12 month old. Now she's suddenly had a growth spurt; she's putting on both height and weight! Her pediatrician is very impressed!
No, neither of them have been diagnosed with celiac disease....but they are both obviously doing better off gluten.
Incidentally, we found out quite by accident that my husband has celiac disease too! After being gluten free for a month he tried drinking some beer and WHAMMO! And he never had ANY symptoms before going gluten free.
Obviously you aren't completely convinced that the right thing to do is to put your son back on gluten, or you would not have posted.
You probably know all of the reasons that celiacs must avoid gluten, even if they never have any symptoms (extra risk of developing other autoimmune diseases, risk of cancer, etc.). But consider also that, if he is celiac, your son's ultimate size and health as an adult man may be determined by what happens now, during this crucial growth period. Putting him back on gluten may harm him; keeping him off gluten is not harmful in any way.
I wish you and your family the best.....