Can β-Hydroxybutyrate Be Detected at the Bedside by In Vitro Oxidation with Hydrogen Peroxide?

Abstract

The diagnosis of ketoacidosis with an inordinately high plasma and urinary concentration ratio of beta-hydroxybutyrate (beta-OHB) to acetoacetate (AcAc) is difficult, because only AcAc and acetone react with the diagnostic reagents used clinically to detect ketones. The purpose of this study was to assess the validity of the claim that beta-OHB can be identified with a simple modification of the usual bedside test for ketones, using hydrogen peroxide (H2O2) and Ketostix (Ames Division, Miles Laboratories, Inc., Elkhart, Indiana). Unfortunately, the lowest detectable concentration of urinary beta-OHB was 50 mmol/L, and serum beta-OHB could not be detected at levels less than 100 mmol/L, a clinically irrelevant level. The relative insensitivity, the inapplicability to serum, and the potential hazard of the routine use of 30% H2O2 by practicing physicians or houseofficers render the method of limited value.

Acid-Base Aspects of Ketoacidosis

“…It has been claimed that a few drops of H2O2 can be added to a urine that initially gives a negative test for ketones and that conversion to a posi tive reaction confirms the presence of p-OHB. We have recently shown, however, that the lowest detectable con centration of urinary P-OHB using Ketostix is 50 mmol/1, and the test requires 30% H2O2 [29]. Thus, although a positive test indicates the presence of P-OHB, the relative insensitivity, the inapplicability to plasma, and the po tential hazard of the routine use of 30% peroxide render the method of limited value.…”

“…When ketoacidosis is associated with a markedly high ratio of p-OHB/AcAc, urinary and serum ketone levels may appear to be inappropriately low in relation to the degree of acidosis and to the increase in the anion gap [29]. In this case, a serum lactate measurement may be of considerable value, since, if no other unusual causes of a high anion gap are present, the lactate concen tration subtracted from the presumed increase in anion gap provides an estimate of the total level of ketoan ions.…”

“…much less with acetone (reactivity only about 5-20% of that of AcAc), and none at all with p-OHB [23][24][25][26][27][28][29]. Ironically, therefore, it measures the ketone body with the lowest plasma concentration during ketonemic states.…”

“…Thus, although a positive test indicates the presence of P-OHB, the relative insensitivity, the inapplicability to plasma, and the po tential hazard of the routine use of 30% peroxide render the method of limited value. If the simple test with H2O2 is negative, the clinical laboratory should be requested to perform Hart's test, which in our hands detects a level of P-OHB of 10 mmol/1 [29].…”

“…Ironically, therefore, it measures the ketone body with the lowest plasma concentration during ketonemic states. Acetest tablets detect both AcAc and ace tone, but Ketostix detects only AcAc [25,26,29,30], To give a strongly positive Acetest reaction the concentra tions of AcAc must be approximately 5.0 mmol/1 or greater [25,26,29]. Enzymatic or nuclear magnetic resonance assays specific for the measurement of AcAc and p-OHB are expensive, relatively time-consuming, and not available in most clinical laboratories [31,32], These considerations are important for the following reasons: (1) Under normal postabsorptive conditions, the serum concentrations of p-OHB, AcAc, and acetone arc between 0.01 and 0.10 mmol/1 [14,17], In DKA, rapid oxidation of FFA increases hepatocyte NADH at the expense of NAD.…”