Ketones
Detection of ketones in urine and blood is used in the management of diabetes mellitus. American Diabetes Association criteria for diabetic keotacidosis include plasma glucose ?250 mg/dL, serum anion gap >10 mEq/L, bicarbonate ?18 mEq/L, blood pH?7.30 and ketosis. Other conditions that can produce elevated levels of ketones include malnutrition, starvation, alcoholism, and some inborn errors of metabolism.
Ketone bodies are catabolic products of free fatty acids and are normally present in urine and blood at very low concentrations. The two major mechanisms for increased ketone levels in patients with diabetes are increased production from triglycerides and decreased utilization by the liver, both due to relative or absolute insulin deficiency.
The three ketone bodies are acetoacetate (AcAc), acetone, and beta-hydroxybutyric acid (BHB). Normally, AcAc and BHB are present in approximately equimolar amounts. Acetone is derived from the breakdown of AcAc and is present in much lower concentration. In all of the disease states associated with ketosis, the equilibrium between AcAc and BHB is shifted toward BHB formation. The typical diabetic patient with ketoacidosis usually has 78% beta-hyroxybutyrate, 20% acetoacetate, and 2% acetone.
For years, ketoacidosis was diagnosed and monitored with a nitroprusside-based test, commonly known as the Acetest. This test measures only AcAc and to a lesser extent acetone but does not detect BHB. Thus, Acetest is relatively insensitive for detecting the early stages of ketoacidosis.
Many laboratories have replaced the Acetest with BHB. The test is performed on a drop of whole blood obtained by fingerstick. Reference range is <0.6 mMol/L.
