Ferric chloride test is positive in –
**Core Concept**
The Ferric chloride test is a chemical reaction used to detect the presence of certain compounds in a sample, particularly in urine or blood. It involves the addition of ferric chloride to the sample, resulting in a color change that indicates the presence of a specific compound.
**Why the Correct Answer is Right**
The Ferric chloride test is positive in the presence of phenylketonuria (PKU). This is because PKU is a genetic disorder that results in the accumulation of phenylalanine in the body, which is then converted to phenylpyruvic acid. The ferric chloride test reacts with phenylpyruvic acid to produce a greenish-blue color. This reaction is specific to the presence of phenylpyruvic acid, making the Ferric chloride test a useful diagnostic tool for PKU.
**Why Each Wrong Option is Incorrect**
**Option A:** Glucose - The Ferric chloride test is not typically used to detect glucose in urine or blood, and glucose does not produce a positive reaction with ferric chloride.
**Option B:** Bilirubin - Bilirubin can produce a positive reaction with ferric chloride, but the reaction is not specific and can be seen in other conditions as well.
**Option C:** Uric acid - Uric acid does not produce a positive reaction with ferric chloride.
**Clinical Pearl / High-Yield Fact**
The Ferric chloride test is a simple and inexpensive screening tool for PKU, but it is not definitive and should be followed up with more specific tests, such as the Guthrie test or tandem mass spectrometry.
**Correct Answer:** D.