Current concepts in the biochemical assessment of the patient with acromegaly

Abstract

Biochemical assessment of a patient for acromegaly aims to definitively establish or exclude the presence of growth hormone excess. Whether applied to a newly recognized patient or to detect residual disease after therapy, this assessment is best accomplished by measurement of both the degree of GH suppression after oral glucose administration (OGTT) and levels of the GH dependent peptide, insulin-like growth factor I (IGF-I). When measured properly and compared to a well-characterized, age-adjusted normative database, elevation of the serum IGF-I level is a sensitive and specific indicator for the presence of acromegaly or persistent disease after therapy. The diagnosis of acromegaly can be confirmed by documenting an elevated IGF-I level in combination with failure of GH to suppress after oral glucose to below 0.3 microg/l, when GH is measured with a highly sensitive and specific assay. Persistently, normal IGF-I levels along with a nadir GH <0.3 microg/l should exclude the diagnosis. In assessing disease status during or after treatment, normalization of IGF-I is an essential criterion for biochemical control. It is important to recognize that nadir GH levels are >0.3 microg/l in some healthy subjects, so this criterion alone is not diagnostic of acromegaly. Also, because of heterogeneity of clinically available GH assays, this GH criterion, which was developed with a research assay, may not be applicable to use with all other assays. A nadir GH cut off of 1 microg/l has been found to be reliable for use with some standard immunoassays. It is recommended that glucose-suppressed GH levels be interpreted in conjunction with those of IGF-I and with consideration of conditions other than acromegaly that can alter them. With greater assay standardization and the use of IGF-I levels along with new rigorous criteria for interpretation of GH suppression during a OGTT we can improve our identification of patients with acromegaly in earlier stages of the disease as well as better recognize residual disease during therapy.