Q&A column

Editor: Frederick L. Kiechle, MD, PhD

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Q. What is the best method to quantify ketones in serum? Can urine strips be used to detect ketones in serum?

A.March 2023—The body’s primary source of energy is carbohydrates. When this pool is depleted, the body begins to use fat to meet its energy needs. The citric acid cycle is the primary process for breaking down fats into energy. When the capacity of the citric acid cycle is exceeded, ketone bodies are formed. The human body goes into a state of ketosis when the concentration of ketone bodies is higher than normal. The three ketone bodies that compose ketosis are beta-hydroxybutyrate (BHB, 78 percent), acetoacetate (20 percent), and acetone (two percent). BHB not only increases during periods of starvation but also during hypoglycemic episodes. Acetoacetate is present in significantly lower concentrations than BHB and is unstable. It spontaneously converts to carbon dioxide and acetone.

BHB is not only the predominant ketone but also the most sensitive and specific marker for assessing ketosis in diabetic ketoacidosis. Under normal circumstances, the ratio of BHB to acetoacetate is 1:1, but the ratio can be 10:1 or higher in ketoacidosis. BHB increases more rapidly in blood during ketogenesis than either acetoacetate or acetone and thus is a better marker for ketosis.

For the aforementioned reasons, the best ketone to quantify is BHB. The enzymatic method is most commonly used for this purpose. It is the best method because of its specificity. However, continuous ketone monitoring devices that measure BHB using enzyme electrochemistry are being evaluated.¹ Urine test strips for measuring ketones use a nitroprusside reagent that reacts well with acetoacetate but not BHB. Therefore, they are not as helpful as the enzymatic BHB method.^2,3 Furthermore, urine test strips may need to be validated if serum is used for measurement, as this is an off-label use. Review the manufacturer’s package insert to determine if validation is needed.

1. Zhang JY, Shang T, Koliwad SK, Klonoff DC. Continuous ketone monitoring: a new paradigm for physiologic monitoring. J Diabetes Sci Technol. 2021;15(4):775–780.
2. Vanelli M, Chiari G, Capuano C, Iovane B, Bernardini A, Giacalone T. The direct measurement of 3-beta-hydroxy butyrate enhances the management of diabetic ketoacidosis in children and reduces time and costs of treatment. Diabetes Nutr Metab. 2003;16(5–6):312–316.
3. Laffel LMB, Wentzell K, Loughlin C, Tovar A, Moltz K, Brink S. Sick day management using blood 3-hydroxybutyrate (3-OHB) compared with urine ketone monitoring reduces hospital visits in young people with T1DM: a randomized clinical trial. Diabet Med. 2006;23(3):278–284.

Stanley F. Lo, PhD, DABCC
Associate Director, Clinical Laboratory
Technical Director, Clinical Chemistry andPoint-of-Care Testing
Children’s Wisconsin
Milwaukee, Wis.
Member, CAP Clinical Chemistry Committee

Q. Is it acceptable to run hemolyzed specimens for coagulation testing? We have a Stago analyzer for coagulation testing and some of my co-workers run hemolyzed specimens on it.

A.It is common for hyperbilirubinemia, hyperlipidemia, and hemolysis to adversely affect laboratory analyses. Their impact is variable and sometimes unpredictable, and it most frequently results from interference with optical detection methods.

Test manufacturers sometimes address the effects of interfering substances on their tests. However, it is ultimately the laboratory’s responsibility to be aware of the effects and impact of these substances.

The consequences of hemolysis on hemostasis testing depend on the test or analyzer used and the degree of hemolysis in the specimen. Coagulation analyzers employ optical or mechanical detection methods. Hemolyzed specimens may interfere with optical-based tests if the detection wavelength overlaps the absorbance spectrum of free hemoglobin. Mechanical-based tests are generally less susceptible to interference by hemolysis, but studies have shown that high concentrations of dissolved hemoglobin falsely prolong clotting times when using mechanical methods.^1,2 One must remember that hemolysis will spill not only free hemoglobin but also phospholipids.

It is important to consider the type of test and whether the manufacturer or others have performed interference studies on the analyzer. For example, hemolysis does not appear to significantly affect prothrombin time and fibrinogen on the Stago STA Compact Max analyzer, but it shortens activated partial thromboplastin time.³