Poor specificity of low growth hormone and cortisol levels during fasting hypoglycemia for the diagnoses of growth hormone deficiency and adrenal insufficiency

OBJECTIVES. Fasting tests are used to identify the cause of hypoglycemia in children. The purposes of this study were to (1) determine whether growth hormone and cortisol levels obtained at the time of hypoglycemia in such tests can identify children with growth hormone and/or cortisol deficiency and (2) identify potential clinical factors that influence growth hormone and cortisol responses to hypoglycemia. STUDY DESIGN. The design consisted of chart review of all diagnostic fasting tests conducted over a 3-year period (n = 151). A normal growth hormone level was defined as >= 7.5 ng/mL, and a normal cortisol level was defined as >= 18 mu g/dL. RESULTS. During the fasting tests, 84 children (median age: 1.3 years [2 days to 14.3 years]), became hypoglycemic, with blood glucose <= 50 mg/dL. Diagnoses included normal, ketotic hypoglycemia, hyperinsulinism, fatty acid-oxidation defects, glycogen-storage disease, and late dumping hypoglycemia. A total of 70% had growth hormone and cortisol levels less than the normal thresholds regardless of diagnosis. Of various factors (age, diagnosis, fast duration, duration blood glucose level of <60 mg/dL, and blood glucose nadir), only age was positively associated with cortisol, and none were consistently related to growth hormone. CONCLUSIONS. A singe low growth hormone or cortisol value at the time of fasting hypoglycemia has poor specificity for the respective diagnoses of growth hormone deficiency and adrenal insufficiency.