The sodium cyanide nitroprusside test is a classical qualitative test widely used in analytical and clinical chemistry to detect the presence of ketone bodies, especially acetone and acetoacetic acid, in biological fluids like urine. This test plays a vital role in diagnosing metabolic conditions such as diabetic ketoacidosis (DKA) and starvation ketosis.
What is the Sodium Cyanide Nitroprusside Test?
The test is based on a chemical reaction between ketone bodies and a mixture of sodium nitroprusside and sodium cyanide under alkaline conditions. When ketone bodies are present, a characteristic purple or maroon color develops, indicating a positive result.
Chemical Principle
Sodium nitroprusside acts as a chromogenic reagent.
Sodium cyanide enhances the sensitivity of the test by forming a more reactive intermediate.
Under alkaline conditions, acetoacetic acid (and to some extent, acetone) reacts with the reagent to produce a colored complex.
β-hydroxybutyric acid is not detected by this method.
Reagents Required
Sodium nitroprusside solution (typically 5% in water)
Sodium cyanide (used carefully due to its toxicity)
Ammonia solution or sodium hydroxide (alkalizing agent)
Test sample (usually urine)
Test Procedure
Add a few drops of the urine sample into a clean test tube.
Add an equal volume of freshly prepared sodium cyanide solution.
Let it stand for 1–2 minutes.
Add a few drops of sodium nitroprusside solution.
Add a few drops of ammonia or sodium hydroxide.
Observe the color change.
Positive Result: A deep purple or burgundy color indicates the presence of ketone bodies.
Applications
Medical Diagnosis: Primarily used to detect ketoacidosis in diabetic patients.
Metabolic Screening: Helps in evaluating starvation, fasting, or low-carbohydrate diets.
Toxicology: May support diagnosis in certain poisoning or metabolic disturbances.
Laboratory Research: Used in biochemical studies of metabolic pathways involving ketones.
Safety Note
Sodium cyanide is highly toxic and should be handled in a well-ventilated fume hood, with appropriate PPE (gloves, goggles, lab coat). Proper disposal procedures must be followed according to institutional and environmental guidelines.