Exploring the clinical utility of blood ketone levels in the emergency department assessment of paediatric patients

Abstract

Determining how sick a child is when he or she attends an emergency department can be challenging. Assessment is usually based on a “snap shot” built on history and examination findings. At the extremes of illness severity, the decision to admit or discharge is usually self‐evident. However, there is a group of children in whom this decision is difficult to make on the basis of history and examination findings alone.¹²³ As clinicians, we are often looking for simple tools or tests that can help us in the assessment of these children.³⁴⁵⁶⁷⁸ These may include the use of scoring systems, bedside investigations or the judicious use of more sophisticated tests.

Scoring systems for severity of illness or risk of admission include the Paediatric Risk of Mortality Score,⁹ the Yale Observation Scale, Odyrons Score for Sick Children and, more recently, the Pediatric Risk of Admission (PRISA) score.¹²¹⁰ These scores are often complicated and time consuming or not easily used prospectively, making their use in the emergency department difficult.²¹⁰¹¹ Bedside or point of care testing (POCT; eg, pulse oximetry, blood glucose testing, electrocardiograms, bedside spirometry and urine analysis) is usually minimally invasive, easy to obtain, provides rapid and relatively accurate results that can influence management, and is cost effective. More sophisticated laboratory tests and imaging modalities are generally expensive and time consuming, and should be reserved for assessment of appropriate patients at the discretion of the attending doctor. Additional information about the scoring system using the PRISA score is available online at http://www.emj.bmjjournals.com/supplemental.

Anecdotally, we have noticed that ketonuria is a common finding in children who are ill, but have not been able to quantify this with accuracy. Ketone bodies are produced by fatty acid metabolism in hepatic mitochondria during a range of physiological and pathological conditions associated with either altered glucose metabolism or relative glucose or glycogen deficiency. There are three ketone bodies: acetoacetate (AcAc), acetone and β‐hydroxybutyrate (β‐HB). Ketones are used primarily by the heart, kidney, central nervous system and skeletal muscle. These tissues produce the enzyme succinyl coenzyme A‐oxoacid transferase.¹² This enables the production of acetyl coenzyme A from ketone bodies and ultimately ATP via the tricarbocylic acid cycle. In toddlers and young children, hyperketonaemia becomes apparent within 12–24 h of a fast. Children of this age are more susceptible to ketosis because of their diminished stores of glycogen and their proportionately larger central nervous systems than adults.¹²

Standard dipstick urine analysis using Ketostix or Multistix (Bayer Diagnostics, Berkshire, UK) gives a semiquantitative measure of AcAc and, to a lesser degree, of acetone.^12131415 It is, however, commonly assumed that β‐HB is quantitatively and clinically the more important ketone body. The ratio of β‐HB to AcAc can vary from 1:1 (postprandially) to 10:1 depending on the physiological status of the patient.^12131415 Urine AcAc levels may underestimate the severity of ketosis.¹²¹⁴¹⁵ Laboratory measurement of β‐HB is not routinely available and takes too long to be of practical use in the emergency department setting. The advent of hand‐held blood ketone meters, more commonly used for testing in patients with diabetes, provides a method for rapid and accurate quantification of blood β‐HB levels. Using techniques similar to that for bedside glucose estimation, one drop of blood on a test strip can provide a ketone level in about 30 s.

This is a simple test that has been well researched in people with diabetes,^1214151617 but also has potential applications in the assessment of a much broader case mix of medical patients in the paediatric emergency department.

Acknowledgements

Abbreviations

Footnotes