Measurement of serum growth hormone (GH) and insulin-like growth factor-I (IGF-) is used to monitor the degree of improvement that occurs following treatment of patients with acromegaly. Improvement in GH assay sensitivity has led to changes in the definition of normal GH however many studies that assess the predictive value of GH were conducted in an era where assays were less sensitive. Other problems that have occurred with GH measurements include utilization of different standards and failure to prove commutability of commonly accepted standard. GH reference ranges vary in their quality and are not stratified for age, sex or body mass index. IGF-I measurements are associated with similar problems. They do not use a common standard that has been proven to be commutable and results can vary widely when the same specimens are assayed in different laboratories. Although age and sex stratified reference ranges exist, these do not always have adequate numbers of subjects and BMI adjusted ranges are not available. These problems have led to significant discordance in a significant number of patients wherein the IGF-I and GH values may yield a discrepant prediction of disease stabilization. In these cases in general the IGF-I values correlate better with the presence of persistent symptoms. Patients who fail to suppress GH to normal but have a normal IGF-I have to be monitored carefully for recurrence but usually do not require further therapy if they are asymptomatic. For the long term assessment of outcome and clinical disease activity measurement of both hormones is recommended.
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