**Core Concept**
The Guthrie test is a bacteriological test used for the early detection of congenital infections, specifically **phenylketonuria (PKU)**, in newborns. It involves the measurement of phenylalanine levels in the blood, which is elevated in individuals with PKU due to a deficiency of the enzyme **phenylalanine hydroxylase**.

**Why the Correct Answer is Right**
The Guthrie test is a bacterial inhibition assay that detects the presence of phenylalanine in the blood, which is converted into a colored compound by the bacterial enzyme **beta-galactosidase**. The test is based on the principle that **Escherichia coli** (E. coli) bacteria are inhibited from growing in the presence of phenylalanine, resulting in a colorless well. If the sample is from a newborn with PKU, the E. coli will grow and produce a color change, indicating a positive result. The Guthrie test is a simple, inexpensive, and reliable method for screening newborns for PKU, allowing for early intervention and prevention of intellectual disability.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because the Guthrie test is specifically designed to detect PKU, not other congenital infections.
**Option B:** This option is incorrect because the test is not based on a biochemical reaction involving **glucose**.
**Option C:** This option is incorrect because the test is not used for detecting **hypothyroidism** in newborns.

**Clinical Pearl / High-Yield Fact**
The Guthrie test is an essential tool for early detection and management of PKU, and it is recommended that all newborns be screened for this condition before discharge from the hospital.

**Correct Answer:** B.