The investigation of hypoglycaemia during childhood

Changes in pediatric plasma acylcarnitines upon fasting for refined interpretation of metabolic stress

BACKGROUND

Childhood fasting intolerance is a life-threatening problem associated with various inborn errors of metabolism. Plasma acylcarnitines reflect fatty acid oxidation and help determine fasting intolerance etiology. Pediatric reference values of plasma acylcarnitines upon fasting are not available, complicating interpretation of stress samples.

METHODS

Retrospective analysis of supervised clinical fasting studies between 01/2005-09/2012. Exclusion criteria involved patients with (suspected) disorders, repeated tests or incomplete results. Remaining children were grouped according to age: group A (≤24 months), B (25-84 months) and C (≥85 months). Median and 2.5^th to 97.5^th percentiles of basic metabolic parameters and acylcarnitines were determined at start and end of testing on the ward and analyzed for significant differences (p<0.05).

RESULTS

Out of 127 fasting studies, 48 were included: group A (n=13), B (n=23) and C (n=12). Hypoglycemia occurred in 21%. Children from group C demonstrated significantly higher end glucose concentrations while end ketone body concentrations were significantly lower compared to younger children. In all groups, free carnitine and C3-carnitine significantly decreased upon fasting, while C2-, C6-, C12:1-, C12-, C14:1-, C14-, C16:1- and C16-carnitine significantly increased. End concentrations of C6-, C12:1-, C12-, C14:1-, C14-, C16:1-, C16- and C18:1-carnitine were significantly lower in children ≥85 months compared to younger children.

CONCLUSIONS

Fasting-induced counter-regulatory mechanisms to maintain energy homeostasis are age-dependent. This influences the changes in basic metabolic parameters and acylcarnitine profiles. Our data enable improved interpretation of the individual fasting response and may support assessment of minimal safe fasting times or treatment responses in patients.

Pediatric hypoglycemia

Hypoglycemia in the pediatric population is a common finding important to recognize and manage to prevent brain injury. Recent advances in molecular genetics have provided new insight into its biochemical and physiologic basis and have led to more appropriate and specific treatment. Although a major cause of brain injury in pediatrics, the ability to predict the long-term outcome in these patients remains difficult. Identification of these at-risk individuals is important. The physiologic adaptations associated with transition from fetal to neonatal life are now better understood thus allowing for improved surveillance and management. Despite these advances, analytical limitations of point-of-care testing instruments at low glucose concentration continue to persist, This review aims to address these questions and provide an overview of pediatric hypoglycemia and the molecular pathways involved.

Update on investigating hypoglycaemia in childhood

Identification and investigation of hypoglycaemia in childhood remains an important clinical emergency. Rapid recognition and appropriate management of this clinical state continues to be important in order to prevent neurological damage or even death. The purpose of this review is to provide an update on the advances made in this area since the review by Bonham in this journal in 1993. Advances in molecular science and diagnostic techniques have assisted in understanding the mechanisms involved in the homeostasis of glucose metabolism at rest and when stressed. New disorders causing hypoglycaemia are described using the classification based upon aetiologies, which was used in Bonham's original paper. The development and use of guidelines and pre-assembled packs for investigating hypoglycaemia is also discussed.

Plasma free fatty acid reference interval in South African neonates in the first week of life

Background

Non-esterified fatty acid (NEFA) levels are an important diagnostic tool in the investigation of neonatal hypoglycaemia. NEFA reference intervals have not been reported for neonates previously.

Methods

The objective of this study was to determine an NEFA reference interval for neonates.

Results

Heparinized plasma obtained from 106 healthy neonates in the first week of life was analysed using the Roche “Free fatty acid, Half-micro test” kit. Results were then analysed statistically for normality (Shapiro–Wilk test) and reference interval determined non-parametrically (bootstrap method).

Conclusions

NEFA levels displayed a non-Gaussian distribution and the reference interval (2.5th and 97.5th percentiles) was 0.2–1.5 mmol/L (90% confidence intervals 0.1–0.3 and 1.4–2.0 mmol/L, respectively). The NEFA reference interval in South African neonates less than a week old is similar to that described in infants (1–12 months), indicating that this reference range can be used over the entire neonatal period.

Audit of acute hypoglycaemia in children: re-audit of procedures for diagnosis

Background

A protocol exists for the collection of samples to investigate unexplained hypoglycaemia, termed the ‘hypopack’. These packs are kept in Accident and Emergency departments and neonatal special care baby units throughout Northern Ireland and most wards of the Regional Children's Hospital. A retrospective audit of 107 hypopacks received between July 2001 and December 2003 highlighted a number of problems: samples collected when the patient was receiving dextrose, incomplete clinical history provided, insufficient and haemolysed samples received and poor filing of reports in charts. These were addressed by re-designing the request form, updating the protocol and introducing a summative report. The new protocol was introduced in April 2006.

Methods

The aim of this study is to assess whether the revised protocol improved utility of the hypopack. A retrospective re-audit of 100 hypopacks received between April 2006 and May 2007 was performed.

Results

Forty-nine percent of patients were hypoglycaemic (<2.6 mmol/L) compared with 35% in the original audit. In both audits, 33% of laboratory reports were missing from patients' charts. One case of medium-chain acyl-CoA dehydrogenase deficiency, three cases of hyperinsulinism and two endocrine-related cases were identified.

Conclusions

The new hypopack protocol has increased the number of appropriately performed investigations. Provision of information concerning dextrose infusion has assisted the interpretation of the hypopack results.

Best practice No 173: clinical and laboratory investigation of adult spontaneous hypoglycaemia

Adult spontaneous hypoglycaemia is not a diagnosis per se but a manifestation of a disease. Although rare, it is important to identify spontaneous hypoglycaemia and its causes because treatment may be preventative or curative. Hypoglycaemia can occur as an epiphenomenon in many serious diseases. It is sufficient to recognise the disease's association with hypoglycaemia and then take appropriate action to prevent the recurrence of hypoglycaemia. In investigating apparently healthy individuals, common pitfalls to avoid are: failure to recognise subacute neuroglycopenia clinically; failure to document hypoglycaemia adequately during symptoms; failure to measure pancreatic hormones, counter-regulatory hormones, and ketones in hypoglycaemic samples; failure to recognise pre-analytical and analytical limitations of laboratory assays; and failure to abandon obsolete and inappropriate investigations. Providing these caveats are met, appropriate laboratory and radiological investigations will almost always uncover the cause of spontaneous hypoglycaemia.

Investigation of the mechanisms of therapy-related hypoglycaemia in children with acute lymphoblastic leukaemia

AIM

To determine the mechanisms of fasting hypoglycaemia occurring during maintenance therapy (MT) for childhood acute lymphoblastic leukaemia (ALL).

METHODS

Thirty-five children and adolescents with ALL, aged 2.4-17.4 y, were fasted for up to 16 h during MT. Nineteen of the children developed hypoglycaemia after 11 to 16 h of fasting. Blood samples for determination of metabolic changes were taken on completion of fasting. Nineteen patients underwent a glucagon stimulation test after 4 to 16 h of fasting during MT. Erythrocyte concentrations of the metabolites of methotrexate (E-MTX) and 6-mercaptopurine (E-TGN) were measured at the time of fasting. Fifteen out of 19 patients who became hypoglycaemic were re-studied 3 to 4 mo after cessation of therapy.

RESULTS

In the hypoglycaemia group, plasma levels of gluconeogenic amino acids alanine and glutamine were lower (medians 117 vs 190 micromol L(-1), p = 0.009, and medians 396 vs 448 micromol L(-1), p = 0.031, respectively) than in the normoglycaemia group. Serum levels of free carnitine were lower (medians 20.3 vs 29.8 micromol L(-1), p = 0.027), free fatty acids higher (medians 3.09 vs 1.23 mmol L(-1), p < 0.001) and marked dicarboxylic aciduria was more common in the patients with hypoglycaemia (in 14/16 vs in 2/14, p < 0.001). Impaired responses to glucagon stimulation occurred in 36% (4/11) in the hypoglycaemia group and in 12.5% (1/8) in the normoglycaemia group (p = 0.243). No significant differences were detected in E-MTX and E-TGN between the groups. Most of the metabolic abnormalities returned to normal after cessation of chemotherapy.

CONCLUSIONS

Low levels of gluconeogenic amino acids, especially of alanine, are associated with hypoglycaemia. Reduced hepatic glycogen stores may also be involved in the aetiology.

Hypoglycemia in childhood: a clinical approach

A child with hypoglycemia presents very frequently an urgent diagnostic and therapeutic challenge. The main causes of hypoglycemia and the clinical approach and laboratory investigations are reviewed underlining that the relationship between the hypoglycemic event and the last meal can aid in diagnosis, in particular for metabolic diseases. Only a correct and precise diagnosis can allow adequate and appropriate treatment and prevention of future hypoglycemic events.

Disorders of mitochondrial long-chain fatty acid oxidation

The oxidation of long-chain fatty acids requires a series of enzymes which are located in or on the mitochondrial membranes. These include carnitine palmitoyltransferases I and II, a carnitine-acylcarnitine translocase and, newly discovered, very long-chain acyl-CoA dehydrogenase and the mitochondrial trifunctional protein. These last two chain-shorten acyl-CoA esters to the point where they can be transferred to the more soluble medium- and short-chain-specific enzymes within the mitochondrial matrix. The disorders of long-chain fatty acid oxidation show a rather similar range of clinical and biochemical features, though with different emphasis in the different conditions. Patients with severe defects usually present early with acute attacks of hypoketotic hypoglycaemia and impaired liver function, or with cardiomyopathy or cardiac arrhythmia. In milder variants, skeletal myopathy with intermittent myoglobinuria develops later in life. 3-Hydroxyacyl-CoA dehydrogenase deficiency is unusual in producing peripheral neuropathy and retinitis pigmentosa. Treatment is based on the avoidance of fasting and replacement of normal dietary fat by medium-chain triglyceride, the medium-chain fatty acids entering the mitochondria in a carnitine-independent manner and bypassing the long-chain part of the spiral. Diagnosis must ultimately be based on direct assay of the enzyme involved, but preliminary indicators may come from determination of carnitine and intermediate metabolites in plasma, urinary organic acid profiling, and radioisotopic screening assays with lymphocytes or cultured fibroblasts.

Comparative frequency and severity of hypoglycemia in selected organic acidemias, branched chain amino acidemia, and disorders of fructose metabolism

The Institution's experience with hypoglycemia in different types of organic acidemias, branched chain amino acidemia (MSUD), and disorders of fructose metabolism was reviewed retrospectively. The charts of 144 patients who were followed for 1-5 years were studied for the severity and frequency of hypoglycemia. The patients were mainly Saudi; however, 10-25% were from neighboring countries. Therefore, the observations pertain to the genetic groups in the Arabian peninsula. Organic acidemias which primarily manifest with neurologic signs, such as 4-hydroxybutyric aciduria, infantile onset 3-methylglutaconic aciduria, and glutaric aciduria type 1 never showed hypoglycemia. Patients with beta-ketothiolase deficiency, biotinidase deficiency, or intermittent or intermediate MSUD, also did not have hypoglycemia during metabolic crisis. Hypoglycemia was rare and mild among neonates with classic MSUD, ethylmalonic aciduria, and isovaleric acidemia. Less than 50% of the patients with MSUD older than 8 months, pyruvate carboxylase deficiency, methylmalonic acidemia, or propionic acidemia had hypoglycemia during metabolic crisis. On the other hand, patients with 3-hydroxy-3-methyl glutaryl-CoA lyase deficiency, holocarboxylase synthetase deficiency, medium or long-chain acyl-CoA dehydrogenase deficiency, neonatal onset 3-methylglutaconic aciduria, glutaric aciduria type 2, and disorders of fructose metabolism invariably had moderate-to-severe hypoglycemia associated with metabolic crisis. The purpose of this report is to provide the pediatrician, particularly in the Middle East, with a diagnostic guideline to the identification and management of different types of organic acidemias, based on co-existing hypoglycemia.