Measuring Beta-Hydroxybutyrate Concentration in Urine

This invention relates to the measurement of beta-hydroxybutyrate in urine.

Accurate measurements of beta-hydroxybutyrate concentration are invaluable in diagnosing certain types of acidoses, e.g., alcoholic acidoses, and acidoses induced by starvation, asphyxia, ketosis, or hyperosmolar, hyperglycemic, non-ketotic coma.

The Hart test, described in Clinical Laboratory Methods Bauer, Ackermann, and Toro, editors (C. V. Mosby Co., St. Louis, 1974) is used to measure beta-hydroxybutyrate and involves adding equal volumes of dilute acetic acid and water to a 20 ml urine sample. The acidified urine is boiled to half its volume to remove acetone/acetoacetate, and is then cooled. Next, hydrogen peroxide and additional water are added, and the solution is warmed and cooled again. This second heating converts the beta-hydroxybutyrate to acetone and acetoacetate, whose presence is detected colorimetrically by adding nitroprusside solution, acetic acid, and ammonia.

My invention provides a simple, rapid method for the measurement of the beta-hydroxybutyrate concentration in a very small urine sample. By the simultaneous use of hydrogen peroxide and of heat of about 100.degree.0 C., the steps of vaporizing the pre-existing acetone/acetoacetate and of converting beta-hydroxybutyrate to acetone/acetoacetate can be performed in a single operation without the addition of acid. Acetone/acetoacetate is released after 8-13 minutes of heating, and beta-hydroxybutyrate is oxidized in 20-30 minutes, so that, after 20 to 28 minutes of heating, all of the originally-present acetone/acetoacetate (which would interfere with the test) has been eliminated, and all of the beta-hydroxybutyrate has been oxidized but not vaporized (as it would be if heating continued).

The method of the invention detects beta-hydroxybutyrate concentrations as low as 5 mM, and gives graded measurements over the range 5-35 mM, within which range have occured clinical beta-hydroxybutyrate levels associated with various acidoses.

One drop of 30% hydrogen peroxide was added to a test tube containing ten drops of a urine sample. The test tube was then placed in a gently boiling water bath for 28 minutes. Any pre-existing acetone/acetoacetate was released as volatile acetone and carbon dioxide after approximately 13 minutes, and after 28 minutes any beta-hydroxybutyrate was oxidized to acetone and acetoacetate.

The test tube was then cooled, and acetone/acetoacetate measured using the nitroprusside test. This gave an accurate measure of beta-hydroxybutyrate originally present in the sample.