While rare, it is possible to have a negative blood test and still have celiac disease. tTG sensitivity is approximately 98%, which means that 2% of all celiacs may have a normal tTG level. Sometimes tTG antibodies are not produced enough to show up in the blood stream and can only be detected in the intestinal mucosa by special means.
IgA deficiency is a reason why you might have a negative blood test, but a positive biopsy.
Further medical evaluation is important for anyone still experiencing symptoms in order to establish the diagnosis or to rule out celiac disease as a part of establishing another diagnosis. In some cases, celiac disease is the wrong diagnosis as such conditions as Crohn’s Disease and food protein allergy share many of the same symptoms
. March, 2016