Legal's exam
Legal's test is used to detect ketone bodies in the urine.
Ketones in urine:
3-Hydroxybutyric acid (β-hydroxybutyric acid, hydroxybutyrate), which is often classified as a ketone body, is not actually a ketone body and therefore cannot be demonstrated by the Legal reaction.
The principle of the test[edit | edit source]
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.
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.[1]
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.[2]
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