**Question:** An infant presented to the OPD with a history of vomiting and poor feeding. Musty odor is present in the baby's sweat and urine. Guthrie test was done and it was found to be positive. All are true regarding this disease except:

A. Guthrie test is negative.
B. The disease is caused by an infectious agent.
C. The infant is not vomiting.
D. The disease has no effect on the baby's urine.

**Correct Answer:** A. Guthrie test is negative.

**Core Concept:** Guthrie test is a screening test used to detect certain genetic and neurometabolic disorders in newborn infants. It involves collecting a بقعة دم (a small piece of filter paper) from the baby's heel and testing it for certain biomarkers that indicate specific diseases. In this case, a positive Guthrie test indicates the presence of certain genetic or neurometabolic disorders in the infant.

**Why the Correct Answer is Right:** A negative Guthrie test would not support the diagnosis of the disease described, as the positive test result is consistent with the presence of genetic or neurometabolic disorders. In this question, the Guthrie test is positive, which supports the diagnosis of the disease with features like vomiting, poor feeding, and musty odor in the urine and sweat.

**Why Each Wrong Option is Incorrect:**

A. Guthrie test is positive for the disease, so a negative test result contradicts the diagnosis.

B. The disease is caused by an infectious agent, but the question states that the disease is genetic or neurometabolic in nature. Therefore, this option is incorrect.

C. Vomiting and poor feeding are clear symptoms of the disease, so stating that the infant is not vomiting contradicts the information provided in the question.

D. The disease causes specific features like musty odor in urine and sweat, which are present in the question. Therefore, this option is incorrect.

**Clinical Pearl:** The Guthrie test is an important tool in neonatal screening for genetic and neurometabolic disorders. Identifying a positive test result in a newborn can initiate further diagnostic investigations, which can lead to early diagnosis and intervention, improving the child's prognosis and overall health outcomes.