Testing for Ketones in the Urine
Testing for ketone bodies is based on a nitroprusside reaction. Acetoacetic acid reacts with sodium nitroferricyanide and glycine in an alkaline medium to produce a violet-to-purple colored complex. The urine chemical reagent strip method can detect as little as 5 mg/dL acetoacetic acid in urine. It does not react with acetone unless glycine is present or B-hydroxybutyric acid. Since these two compounds are derived from acetoacetic acid, their presence can be assumed if the test for ketones is positive.
Ketones are reported either as negative, small, moderate or large amounts; or negative, 1+, 2+, 3+, or 4+. In some severe cases of ketosis, it may be necessary to perform tests on serial dilutions to provide more information on the quantity of ketones present.