Final answer:
A confirmatory test for lactose intolerance is often necessary when initial testing suggests the condition. The hydrogen breath test is a primary diagnostic tool used to measure undigested lactose. An intestinal biopsy or stool acidity test for infants is used less commonly.
Step-by-step explanation:
A confirmatory test for lactose intolerance is typically necessary when an initial test, such as lactose intolerance symptoms or the hydrogen breath test, suggests the presence of the condition. The hydrogen breath test is a primary diagnostic tool where the patient consumes a lactose solution after fasting, and the hydrogen gas in their breath is measured. Elevated levels of hydrogen indicate that lactose is not being properly digested and is instead fermented by bacteria in the colon. In some cases, an intestinal biopsy may be done to measure lactase enzymes or mRNA in the tissue, although this is not common due to the need for specialized laboratories.
Lactose intolerance can also be diagnosed in infants using the stool acidity test. For infants at risk or when other tests are impractical, the presence of acid in the stool indicates undigested lactose. Additionally, dietary adjustments, including lactose-free dairy products and dietary supplements providing lactase, can help manage lactose intolerance. In cases of lactose intolerance type II, caused by galactose-1-phosphate uridyl transferase deficiency, lactose-free milk is necessary to prevent symptoms like diarrhea and vomiting.