IgG tests promise to reveal food sensitivities. But are they science or science-ish?

https://healthydebate.ca/2017/01/topic/igg-tests-science/ 

That’s a problem for IgG tests, because IgG is an immune response. And in studies on lessening allergic reactions to things like milk or peanuts, researchers have found that IgG levels go up as the severity of an allergic reaction goes down. It’s thought that we produce the most IgG antibodies to foods that we eat regularly—“like getting a constant booster shot,” says allergist Stuart Carr. That’s why common foods, like dairy, wheat and egg, will often show up positive on an IgG test.

Kirste says that message resonates with her clients. “I’ll tell them that IgG may simply indicate that the food is in the diet. And we know that in children who are outgrowing an allergic condition, IgG goes up, and IgE goes down,” she says. “Then the light bulb goes on—they get it.”

Across the country, Carr is having similar conversations. He says he often has people who have had IgG tests get referred to him – and he has to explain to them that they’ve paid big bucks for something that offers no useful information. “When I see a patient come into my clinic, and they say we had this [IgG] test done, they will reach in their bag and try to hand me this booklet of results,” he says. “I’ll say, I don’t need to see that, and explain why we can ignore it.”

And a more recent review on allergy management and diagnosis published this fall in the CMAJ also expressed concerns about them. “Food-specific immunoglobulin G (IgG) testing is being increasingly used to identify food ‘sensitivities,’” it reads. “… In fact, food specific IgG is to be expected, marking the presence of exposure and tolerance to a food.”