Never, in fact. Other variables must be part of a diagnosis. New guidelines in 2011 allow for diagnosis without a biopsy, but only in very rare cases. In these rare cases at least one of the genes must be present, both tTG and EMA blood tests must be more than 10x normal, and there must be a positive response to a gluten-free diet.
Because the above cases are so rare, the gold standard for diagnosis is still an endoscopic biopsy of the small intestine.
Read our 2012 Q1 Newsletter, “Evolving Diagnostic Criteria for Celiac Disease
,” to learn more. March, 2016