Why is hydrogen breath test referred to as the "gold standard"?

Hydrogen breath test: It is gold standard because it is the old and reliable test used todiagnose fructoce and lactose intolerance, and bacterial overgrowth syndrome and no other test comes close to it.But having said that the standardisind and interpretation of the test still remains difficult.

It's good: Gold standard means that the test mentioned is considered to be the best possible test for that specific medical problem.