Make sure they checked all of the following while using the blood test: total IgA, IgA and IgG gliadin, transglutaminase and endomysial titers. Even with all of those, there's a high possibility of getting a negative result that is incorrect. Please check farther, just to be sure.
They checked for celiacs with the bloodtest but they didn't say anything about false negetives for it so thanks for the info.
A thought - has he been tested for celiac disease - checking his genes? You can do it yourself instead of going to the doc and it just might give you an answer. Blood tests looking for antibodies don't always give 'true' negatives for this disease. You could check with enterolab.com about the allele test. I think it runs about $150.00. If he turns up positive, despite the results of what can be seen in a blood test, changing his diet could change things around.
Celiac disease can result in 'ploppy' stools that smell awful.