Laboratory studies in growth hormone deficiency (GHD) include the following:
Thyroxine and thyroid-stimulating hormone: Hypothyroidism should be excluded as a cause of growth failure and short stature.
Serum electrolytes: A low bicarbonate level may indicate renal tubular acidosis, which can result in growth failure. Abnormal electrolytes may indicate renal failure.
CBC count and sedimentation rate: These studies may be helpful if inflammatory bowel disease is suspected.
Insulinlike growth factor 1 (IGF-1) and IGF-binding protein 3 (IGFBP-3)
- Both IGF-1 and IGFBP-3 are growth hormone–dependent.
- Low values of IGF-1 and IGFBP-3 suggest growth hormone deficiency. However, a low value alone is not diagnostic because IGFs are sensitive to other factors such as nutritional state and chronic systemic disease.
- Girls with otherwise unexplained short stature should have a karyotype study to rule out Turner syndrome.
- Although many girls with Turner syndrome are diagnosed from signs upon physical examination, the only recognizable feature of many girls with the condition is short stature.
- In particular, girls with mosaic karyotypes or karyotypes with isochromosomes tend to exhibit fewer signs specific to Turner syndrome.
- Many girls with Turner syndrome, and particularly those with mosaic karyotypes and karyotypes other than 45,X, do not demonstrate the striking stigmata associated with Turner syndrome.
- Boys in which there is clinical suspicion of a possible genetic etiology of the growth disorder have about the same likelihood of having an abnormal karyotype as is seen in girls being evaluated for Turner syndrome.
Patients diagnosed with growth hormone deficiency should undergo an MRI of the head to exclude a brain tumor (eg, craniopharyngioma). Approximately 15% of patients with growth hormone deficiency have an abnormality of the pituitary gland (eg, ectopic bright spot, empty or small sella).
Comparison of a left hand and wrist radiograph to standards can be used to estimate skeletal maturation. With familial short stature, bone age is comparable to chronological age. Bone age is usually delayed in children with constitutional growth delay, malnutrition, and endocrine causes of short stature (eg, hypothyroidism, cortisol excess, growth hormone deficiency). Bone age also allows determination of growth potential as adult stature may be estimated from the Bayley-Pinneau tables.
Growth hormone response to insulin is the most reliable test for growth hormone deficiency. Before accepting growth hormone deficiency diagnosis, many insurance companies require a documented failure to demonstrate a growth hormone response (with a growth hormone level >10 ng/mL) after presentation of 2 provocative stimuli. Provocative stimuli include insulin-induced hypoglycemia, arginine, levodopa (L-dopa), clonidine, and glucagon.
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