Question

The cyanide nitroprusside reaction detects any compound containing a sulfhydryl group, is used to screen -

• A. Cystinuria
• B. Glucosuria
• C. Aciduria
• D. Proteinuria

Hint:

Cystinuria chemical screening test:
- Reagent: Sodium cyanide (breaks disulfide bonds) + Sodium nitroprusside.
- Positive Result: Cherry-red/purple color indicating free sulfhydryl (\(-\text{SH}\)) groups.
- Microscopic clue: Look for diagnostic hexagonal crystals in urine sediment.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
Qualitative chemical screening tests are used to detect abnormal metabolites or excessive compounds excreted in urine.
The sodium cyanide-nitroprusside test is a classic colorimetric chemical reaction designed to detect sulfur-containing amino acids.

Step 2: Detailed Explanation:
Cystinuria is an inherited metabolic disorder characterized by defective transport of cystine and dibasic amino acids (lysine, arginine, ornithine) in the renal proximal tubules.
This defect leads to excessive excretion of cystine in urine.
Because cystine is relatively insoluble at normal acidic urine pH, it precipitates to form characteristic hexagonal cystine crystals, which can progress to form urinary calculi (stones).
To screen for cystinuria, the cyanide-nitroprusside test is performed on urine:
First, sodium cyanide is added to the urine sample.
The cyanide acts as a reducing agent, breaking the disulfide bond of cystine to convert it into two molecules of the sulfhydryl-containing amino acid, cysteine.
Second, sodium nitroprusside is added to the mixture.
The free sulfhydryl (\(-\text{SH}\)) groups of the newly formed cysteine react rapidly with the nitroprusside in an alkaline medium.
This reaction produces a highly visible cherry-red to purple-magenta color, indicating a positive screening result for cystinuria.
The other options (Glucosuria, Aciduria, and Proteinuria) are screened using different tests, such as Benedict's test, pH indicators, or sulfosalicylic acid tests.

Step 3: Final Answer:
The cyanide nitroprusside reaction is used to screen for Cystinuria.