What substance is tested for in the lactose tolerance test?

In the lactose tolerance test, the primary substance being measured is glucose. This test evaluates how well a person's body can digest lactose, which is the sugar found in milk and dairy products. When a person consumes lactose, healthy individuals will typically break it down into glucose and galactose, allowing glucose to enter the bloodstream. The test measures the level of glucose in the blood after lactose consumption; a significant rise in glucose indicates that lactose was properly digested and absorbed.

The other substances listed are not the focus of this specific test. Fructose, lactate, and sucrose are different types of sugars or byproducts that are related to other metabolic processes and tests, thus making them unrelated to the direct evaluation of lactose absorption.