**Core Concept**
Eijkman's test is a diagnostic tool used to detect the presence of a specific enzyme deficiency. This test is crucial in the diagnosis of certain metabolic disorders. The underlying principle involves the measurement of enzyme activity levels in a patient's blood.

**Why the Correct Answer is Right**
Eijkman's test is specifically used to detect the deficiency of galactose-1-phosphate uridyltransferase (GALT) enzyme, which is essential for the metabolism of galactose. This enzyme catalyzes the transfer of a uridyl group from UDP-glucose to galactose-1-phosphate, converting it to UDP-galactose. Individuals with GALT deficiency are unable to properly metabolize galactose, leading to the accumulation of toxic compounds in the body. Eijkman's test is a reliable method for diagnosing this enzyme deficiency.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because Eijkman's test is not used to detect the deficiency of lactase enzyme, which is associated with lactose intolerance.
**Option B:** This option is incorrect because Eijkman's test is not a diagnostic tool for Wilson's disease, a disorder related to copper metabolism.
**Option C:** This option is incorrect because Eijkman's test is not used to detect the deficiency of a specific enzyme involved in the metabolism of amino acids.

**Clinical Pearl / High-Yield Fact**
Eijkman's test is a crucial diagnostic tool in the management of galactosemia, a genetic disorder that can lead to severe health complications if left untreated.

**Correct Answer: D. Galactosemia**