## **Core Concept**
The Guthrie test is a microbiological assay used for the detection of an amino acid disorder. It is specifically designed to identify elevated levels of a particular amino acid in the blood.

## **Why the Correct Answer is Right**
The Guthrie test is utilized for the diagnosis of **Phenylketonuria (PKU)**, a genetic disorder characterized by the inability to break down the amino acid phenylalanine (Phe). This test works by using a bacterial inhibition assay, where the growth of *Bacillus subtilis* is inhibited by phenylalanine. If phenylalanine levels are high in the blood sample, it will inhibit the growth of the bacteria, indicating a positive result for PKU.

## **Why Each Wrong Option is Incorrect**
- **Option A:** This option is incorrect because, although related to metabolic disorders, it does not specifically correspond to the Guthrie test's application.
- **Option B:** This option is incorrect as it does not relate to the Guthrie test.
- **Option D:** This option is incorrect because it does not accurately represent the condition diagnosed by the Guthrie test.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that early detection of **Phenylketonuria (PKU)** through the Guthrie test allows for early intervention, such as dietary restrictions, which can significantly improve outcomes for patients by preventing intellectual disability and other complications associated with PKU.

## **Correct Answer:** . **Phenylketonuria**