Lactose intolerance in a suspected patient is diagnosed by giving an oral load and measuring concentrations of ?

**Core Concept**
Lactose intolerance is a condition where the body is unable to digest lactose, a sugar found in milk, due to a deficiency of lactase enzyme in the small intestine. This enzyme is responsible for breaking down lactose into easily absorbed sugars, glucose and galactose.

**Why the Correct Answer is Right**
The correct answer is based on the principle of measuring the residual lactose in the small intestine after an oral load, which is indicative of lactose intolerance. When lactose is not broken down by lactase enzyme, it is not absorbed and remains in the small intestine. The concentration of lactose in the small intestine can be measured using a test called the lactose tolerance test or hydrogen breath test.

**Why Each Wrong Option is Incorrect**
* **Option A:** Glucose levels would be elevated in response to the lactose load, but this does not directly measure lactose intolerance.
* **Option B:** Galactose levels would be elevated in response to the lactose load, but this does not directly measure lactose intolerance.
* **Option D:** Lactate levels would be elevated in response to the lactose load, but this does not directly measure lactose intolerance.

**Clinical Pearl / High-Yield Fact**
The lactose tolerance test is a useful diagnostic tool for lactose intolerance, but it is not 100% accurate. The hydrogen breath test is a more sensitive and specific test for lactose intolerance, as it measures the production of hydrogen gas by bacteria in the small intestine when lactose is not broken down.

**Correct Answer: C. Hydrogen.**