**Question:** In phenylketonuria, FeCI test with urine gives ............. color.

**Core Concept:** Phenylketonuria (PKU) is an inherited disorder caused by deficiency of phenylalanine hydroxylase enzyme, which leads to accumulation of phenylalanine and its hydroxylated product, phenylalanine hydroxylase (PAH). The FeCI test is a test used to detect the presence of phenylalanine in urine.

**Why the Correct Answer is Right:** The FeCI test is based on the principle that phenylalanine reacts with ferric chloride to form a purple-colored complex. In PKU, phenylalanine accumulates in the urine, leading to the formation of the purple complex. This test aids in confirming the diagnosis of PKU.

**Why Each Wrong Option is Incorrect:**

A. **Option A:** The correct answer is not related to this option. In PKU, the urine color is not affected, so this option is incorrect.
B. **Option B:** PKU patients should avoid phenylalanine-rich foods to prevent neurodevelopmental issues. However, this option does not address the test's result in PKU patients.
C. **Option C:** PKU patients have elevated phenylalanine levels in urine, which results in the purple complex formation. This option is incorrect as it does not explain the test's result.
D. **Option D:** PKU diagnosis can be confirmed by other tests like newborn screening, blood phenylalanine levels, and urine testing for phenylalanine and its hydroxylated product, phenylalanine hydroxylase (PAH). This option does not address the test's result in PKU patients.

**Clinical Pearl:** The FeCI test is an important diagnostic tool for detecting PKU and confirming the presence of elevated phenylalanine levels in urine. The test demonstrates the purple complex formation, which is indicative of PKU and helps diagnose the condition.

**Correct Answer:** Correct Answer: C. **Option C:** PKU patients have elevated phenylalanine levels in urine, which results in the purple complex formation. This option is incorrect as it does not explain the test's result. However, it highlights the increased phenylalanine levels in urine of PKU patients, which lead to the purple complex formation. This aspect is crucial in understanding the test's outcome in PKU patients.