The correct measurement of an infant’s length requires one adult to hold the infant’s head still and another adult to extend the feet with the soles perpendicular to the lower legs. A caliper-likedevice, such as an infantometer, or the movable plates on an infant scale are used so that the exact distance between the two calipers or plates can be determined. Marking the position of the head and feet of an infant lying on a sheet of paper on the examining table leads to inaccuracies and may miss true disorders of growth or create false concerns about a disorder of growth in a normal child. Accurate measurements of height (standing), or length (lying down), and weight should be plotted on the Centers for Disease Control and Prevention growth charts for the timely diagnosis of growth disorders ( http:// www.cdc.gov/growthcharts/
After 2 years of age, the height of a child should be measured in the standing position. Children measured in the standing position should be barefoot against a hard surface. A Harpenden stadiometer or equivalent device is optimal for the measurement of stature. A decrease of roughly 1.25 cm in height measurement may occur when the child is measured in the standing position rather than in the lying position, leading to the inappropriate referral of many children who appear to be not growing to a subspecialist.
Measurement of the arm span is essential when the diagnoses of Marfan or Klinefelter syndrome, short-limbed dwarfism, or other dysmorphic conditions are considered. Arm span is measured as the distance between the tips of the fingers when the patient holds both arms outstretched horizontally while standing against a solid surface. The upper-to-lower segment ratio is the ratio of the upper segment (determined by subtraction of the measurement from the symphysis pubis to the floor [known as the lower segment] from the total height) to the lower segment. This ratio changes with age. A normal term
Adapted from Underwood LE, Van Wyk JJ: Normal and aberrant growth. In Wilson JD, Foster DW, editors: Textbook of Endocrinology, ed 8, Philadelphia, 1992, WB
Saunders. *Effect in most patients with treatment.
infant has an upper-to-lower ratio of 1.7:1, a 1-year-old has a ratio of 1.4:1, and a 10-year-old has a ratio of 1:1. Conditions of hypogonadism, not commonly discerned or suspected until after the normal age for onset of puberty, lead to greatly decreased upper-to-lower ratio in an adult, whereas long-lasting and untreated hypothyroidism leads to a high upper-tolower ratio in the child.
Endocrine Evaluation of Growth Hormone Secretion
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GH is a 191–amino acid protein secreted by the pituitary gland under the control of GRF and SRIF (see Fig. 170-2). GH secretion is enhanced by α-adrenergic stimulation, hypoglycemia, starvation, exercise, early stages of sleep, and stress and inhibited by β-adrenergic stimulation and hyperglycemia. Because concentrations of GH are low throughout the day, except for brief secretory peaks in the middle of the night or early morning, the daytime ascertainment of GH deficiency or sufficiency on the basis of a single determination of a random GH concentration is impossible. Adequacy of GH secretion may be determined by a stimulation test to measure peak GH secretion. A normal response is a vigorous secretory peak after stimulation; the lack of such a peak is consistent with GH deficiency. However there is a high false-positive rate (on any day, about 10% or more of normal children may not reach the normal GH peak after even two stimulatory tests). Indirect measurements of GH secretion, such as serum concentrations of IGF-1 and IGF-BP3, are considered better screens for GH deficiency.