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The fasting test in paediatrics: application to the diagnosis of pathological hypo- and hyperketotic states
J P Bonnefont1, N B Specola, A Vassault
1Département de Pédiatrie, Inserm U-12, Hôpital des Enfants-Malades, Paris, France.
Insights
A 24-hour fasting test in children revealed that blood glucose, carnitine, and glycaemic response correlate negatively with ketone bodies. Specific ratios and products can help differentiate metabolic disorders in children undergoing fasting tests.
Area of Science:
- Biochemistry
- Pediatric Endocrinology
- Metabolic Disorders
Background:
- Fasting tests are crucial for diagnosing metabolic disorders in children.
- Understanding the body's metabolic response to fasting, including glucose and ketone production, is vital.
- Inherited defects in fatty acid oxidation and ketolysis can impair normal metabolic adaptation to fasting.
Purpose of the Study:
- To investigate the metabolic changes during a 24-hour fasting test in children.
- To identify biochemical markers that differentiate between normal metabolic responses and disorders of ketogenesis and ketolysis.
- To assess the utility of specific metabolic ratios and products in diagnosing hypoketotic and hyperketotic disorders.
Main Methods:
- A 24-hour fasting test was conducted on 48 control children and 21 patients with suspected defects in fatty acid oxidation or ketolysis.
- Blood samples were collected at 15, 20, and 24 hours to measure glucose, lactate, free fatty acids (FFA), ketone bodies (3-hydroxybutyrate and acetoacetate), and carnitine.
- Control children were stratified into age groups based on fasting adaptation.
Main Results:
- Significant negative correlations were observed in controls between plasma total ketone bodies (KB) and plasma glucose (P < 0.001), plasma carnitine (P < 0.005), and glycaemic response to glucagon (P < 0.01).
- The FFA/KB ratio and the product of final fasting glucose and ketones effectively differentiated hypoketotic/hyperketotic patients from normal subjects.
- These findings highlight distinct metabolic profiles during fasting in children with and without specific metabolic defects.
Conclusions:
- The study identifies key metabolic indicators, including glucose, carnitine, and ketone body levels, that change predictably during fasting in children.
- Specific biochemical ratios and products derived from fasting tests can serve as valuable diagnostic tools for inherited disorders of fatty acid oxidation and ketolysis.
- Fasting tests should be performed cautiously in well-nourished children with normal baseline investigations, ensuring sufficient fasting duration for metabolic activation.
Abstract:
A 24-h fasting test was performed in 48 control children, in 9 hypoketotic patients with inherited defects of fatty acid oxidation and in 2 hyperketotic patients with inherited defects of ketolysis. The control group was then divided into three age groups on the basis of different adaptation to fasting. Concentrations of blood glucose, lactate, free fatty acids (FFA), 3-hydroxybutyrate, acetoacetate and carnitine were measured after 15 h, 20 h and 24 h of fasting. Significant negative correlations were found in the control group between plasma total ketone bodies (KB) and plasma glucose (P less than 0.001), plasma carnitine (P less than 0.005) and the amplitude of glycaemic response to glucagon at the end of the fast (P less than 0.01). FFA/KB ratio and the product of final fasting values of glucose and ketones were useful to differentiate between hypoketotic or hyperketotic patients and normal subjects. In children with a suspected or definite hyperketotic or hypoketotic disorder, a fasting test must only be performed in healthy patients, in good nutritional condition with non-diagnostic basal biochemical investigations. Carefully supervised fasting should be continued sufficiently to allow ketogenesis and ketolysis to become activated.