Excessive GH production is chacterized by an elevated serum insulin-like growth hormone factor-1 (IGF-1) and the lack of adequate GH reduction after oral glucose ingestion. Serum IGF-1 concentrations are age and gender dependent. GH secretion and serum IGF-1 concentrations decline with increasing age,
From: Management of Pituitary Tumors: The Clinician's Practical Guide, Second Edition Edited by: M. P. Powell, S. L. Lightman, and E. R. Laws, Jr. © Humana Press Inc., Totowa, NJ
and women have higher levels than men. An accurate IGF-1 assay with a suitable database reflecting normal age- and gender-matched values is the keystone in screening patients with possible acromegaly. An important consideration is the young woman with galactorrhea, menstrual disturbance, and hyperprolactinemia. In this setting, the patient may not have the classic features of acromegaly. Patients with early acromegaly may not have the suggestive features of facial changes, hyperhidrosis, and acral enlargement. Thus, any patient with hyperprolactinemia should be screened for acromegaly by measurement of serum IGF-1. GH-producing pituitary adenomas may also produce excessive prolactin (PRL) (bihormonal tumor or mammosomatotrope tumor). This distinction is essential because the treatment of a prolactinoma and a GH plus prolactin-pro-ducing tumor is different, with medical therapy the first choice for a prolactinoma and surgery for a GH and prolactin-producing tumor. The diagnosis of acromegaly is ascertained by the presence of an elevated serum IGF-1 concentration and the failure of GH to decline to <1 ng/mL (^g/L) (2.5 mU/L) after ingestion of 75 or 100 g of glucose. With the refinement of GH assays with increased sensitivity, this criterion of a GH of <1 ng/mL (^g/L) (2.5 mU/L) has replaced the value of a GH of <2 ng/mL (^g/L) (5 mU/L)(8). It is important that the oral glucose test be performed properly with measurement of GH levels before and every 30 min after glucose ingestion during 120 min (2 h, a total of five blood samples).
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