A Simple and Cost-Effective Approach to Assessment of Pituitary Adrenocorticotropin and Growth Hormone Reserve: Combined Use of the Overnight Metyrapone Test and Insulin-Like Growth Factor-I Standard Deviation Scores

CONTEXT: The insulin tolerance test (ITT) is the gold standard for assessment of ACTH and GH reserve in patients with suspected hypopituitarism. It is labor intensive and costly. OBJECTIVE: The objective of the study was to determine whether use of the overnight metyrapone test (OMT) and plasma IGF-I sd scores (SDS) could provide a cost-effective alternative to the ITT. DESIGN: This was a retrospective chart review. SETTING: The study was conducted at a teaching hospital. PARTICIPANTS AND INTERVENTION: Charts from 100 patients with organic pituitary disorders were reviewed. All underwent the OMT unless 0900 h plasma cortisol was less than 80 or greater than 450 nmol/liter when ACTH deficiency or ACTH sufficiency, respectively, was diagnosed. Patients were considered GH deficient if the age-related IGF-I SDS was less than -3 or if they had three or more other pituitary hormone deficiencies. Patients were considered GH sufficient if age-related IGF-I SDS was greater than the 95th centile established from patients with known GH deficiency. Thirty-three underwent an ITT. MAIN OUTCOME MEASURES: The proportion of patients in whom ACTH and GH reserve could be assessed using OMT/IGF-I SDS was measured. The concordance with results was obtained from ITT. RESULTS: Fifty-five patients were ACTH sufficient and 45 were ACTH deficient. Twenty-one were GH sufficient and 33 were GH deficient based on IGF-I SDS and other pituitary hormone deficiencies, whereas 46 could not be classified. There was near-uniform concordance between OMT/IGF-I SDS and ITT. Initial investigation using OMT/IGF-I SDS resulted in a significant cost saving. CONCLUSIONS: ACTH and GH reserve can be accurately and cost-effectively investigated using OMT/IGF-I SDS in approximately 50% of patients with organic pituitary disorders.