Although the list of causes of hypoglycemia is long and complex, establishing the etiology in a particular patient is important. Frequently it is difficult to make an accurate diagnosis until one can obtain a critical sample of blood and urine at the time of the hypoglycemic episode. In a child with unexplained hypoglycemia, a serum sample should be obtained before treatment for the measurement of glucose and insulin, GH, cortisol, FFAs, and β-hydroxybutyrate and acetoacetate. Measurement of serum lactate levels also should be considered. A urine specimen should be obtained for measuring ketones and reducing substances. Hypoglycemia without ketonuria suggests hyperinsulinism or a defect in fatty acid oxidation. The results of this initial testing can establish whether endocrine causes are responsible and, if not, provide initial information regarding which types of metabolic disorders are most likely. Whenever possible, additional samples of blood and urine should be frozen for further analysis, if necessary.
Acute care of a patient with hypoglycemia consists of rapid administration of IV glucose (2 mL/kg of 10% dextrose in water). After the initial bolus, an infusion of IV glucose should provide approximately 1.5 times the normal hepatic glucose production rate (8 to 12 mg/kg/min in infants, 6 to 8 mg/kg/min in children). This infusion allows for suppression of the catabolic state and prevents further decompensation in patients with certain metabolic disorders. If adrenal insufficiency is suspected, stress doses of glucocorticoids should be administered.
Normal growth is the final common pathway of many factors,including endocrine, environmental, nutritional, and geneticinfluences (see Chapter 5). A normal linear growth patternis good evidence of overall health and can be considered abioassay for the well-being of the whole child. The effects ofcertain hormones on growth and ultimate height are listed inTable 173-1. Just as various factors influence stature, stature itself influences psychological, social, and potentially economic well-being. Parental concern about the psychosocial consequences of abnormal stature often causes a family to seek medical attention.
Growth hormone (GH) secretion is pulsatile, stimulated by hypothalamic GH-releasing factor (GRF) and inhibited by GH release inhibitory factor (somatostatin, somatotropin release-inhibiting factor [SRIF]), which interact with their individual receptors on the somatotrope in a noncompetitive manner. GH is also stimulated by ghrelin, produced in the stomach. GH circulates bound to a GH-binding protein (GHBP); GHBP abundance reflects the abundance of GH receptors. GH has direct effects on tissue and also causes production and secretion of insulin-like growth factor-1 (IGF-1) in many tissues. GH stimulates IGF-1 production in liver along with production of the acid-labile subunit and the IGF-binding protein (IGF-BP3); this forms the complex that delivers IGF-1 to tissue.
IGF-1 acts primarily as a paracrine and autocrine agent and is most closely associated with postnatal growth. When IGF-1 attaches to its membrane-bound receptor, second messengers are stimulated to change the physiology of the cell and produce growth effects. IGF-1 production is influenced by disease states such as malnutrition, chronic renal and liver disease, hypothyroidism, or obesity.
IGF-BP3 is measurable in clinical assays and is less influenced by nutrition and age than is IGF-1; measuring IGF-1 and IGF-BP3 is useful in evaluating GH adequacy, particularly in infancy and early childhood.
Measurement of Growth