How to check for lactose intolerance and gluten allergy?

Depends: Lactose intolerance is mostly a clinical diagnosis--usually leads to GI symptoms after eating foods containing lactose (dairy). Biopsy of the intestine can confirm the diagnosis as well. Celiac disease (gluten sensitivity) can be screened for with blood tests, and the confirmatory test is also a biopsy of the intestine. It's important that these tests be done while you're on a regular diet.