Urinary ketone bodies/determination

The detection of ketone bodies is based on the reactions of acetoacetic acid and acetone with sodium nitroprusside in an alkaline medium, which forms a red-violet-colored complex  . This principle is used by Legal's and Lestradet's exams, as well as diagnostic strips. Β-hydroxybutyric acid (ie the most abundant ketone substance) does not provide a reaction and therefore a negative result does not completely rule out ketoacidosis.

Compounds with free sulfhydryl groups (eg the antihypertensive captopril or uroprotectant used in some mesna chemotherapeutic regimens ) provide false positivity for urinary ketone bodies  . Quite often, bacterial products in urinary tract infections also provide a similar response.

False negatives, apart from the already mentioned insensitivity of the β-hydroxybutyric acid tests, are not significant.