Inter-Assay Growth Hormone and IGF-I Variability

This research will explore the variability of GH and IGF-1 measurements by commercially available tests. The hypothesis is that the variability in GH and IGF-1 measurement will be sizable enough that different conclusions would be drawn in patient case decision making in the diagnosis and management of GH deficiency and acromegaly.

In order to correctly diagnose disorders of growth hormone secretion, either deficiency or excess, it is necessary to have the accurate measurement of GH (growth hormone) serum and Insulin-like growth factor (IGF-1).

For this study, subjects will be asked to give the Investigators additional blood during either an OGTT (a test for acromegaly) or a growth hormone stimulation test (GHRH-arginine stimulation). Ordinarily, blood would be measured at the beginning and end of the OGTT, and for the GHRH-arginine it would be measured one half hour before the test and then every half hour for 2 hours.

For this study, subjects will provide us with additional blood at the times when blood is drawn for the clinically-indicated tests. No additional needle sticks will be necessary and taking the additional blood will not interfere with the clinical test.

The test we will be doing with the additional blood will be identical to the tests we ordinarily do, but will be done by a different lab. We are testing to see if these results would be the same as our usual lab.

The study population will include 1) subjects with pituitary disease undergoing testing for GH deficiency (GHRH arginine stimulation test), 2) subjects with suspicion of acromegaly undergoing the oral glucose tolerance test (oGTT), and 3) normal controls undergoing both the GHRH Arginine test and the oGTT. Patients from all groups will have their blood drawn for the measurement of IGF-1. The serum from each test will be aliquoted and sent to the designated labs.

For subject groups 1 and 2, this study poses no more than minimal risk, as it involves procedures that do not go beyond clinical care. For healthy controls, we know that participants will be asked to undergo testing that would not normally be required, and therefore feel that the study poses more than minimal risk.

For the primary endpoint research samples will be compared to samples sent to the usual clinical lab, and diagnoses made based on research samples will be compared to clinical samples.

For secondary endpoints, each result from a commercially available assay will be correlated to another corresponding method of analysis of the same hormone from the same time point by using the Bland-Altman analysis wherein the difference between two methods is compared to the mean of the two methods. Each sample will be compared to the sample used for clinical evaluation.

Information from the medical records will be obtained and correlated with the lab test results.