Legal's exam

Legal's test is used to detect ketone bodies in the urine.

Ketones in urine:


 * acetone


 * acetic acid


 * 3-hydroxybutyric acid

The principle of the test
The principle is the reaction of ketone bodies (acetic acid and acetone) with sodium nitroprusside in a strongly alkaline environment of sodium hydroxide. The result is a purple colored product.

800px | Průkaz ketolátek v moči

This principle has a number of modifications, mainly when securing an alkaline environment, and all work procedures use it, both in the form of diagnostic strips and in the form of a powder reagent.

False negativity:

3-hydroxybutyric acid is the most abundant in ketoacidosis, which means that even a negative result does not completely rule out ketoacidosis.

False positivity:

Urine containing pigments or metabolites of levodopa (dihydroxyphenylalanine) may give false positive results.

Links
related articles


 * Ketone bodies in the urine


 * Urine ketone bodies/determination

List of literature