Abstract

BOERO, L. et al. Acromegaly: Comparison of serum IGF-1 levels measured by two immunoassays and their correlation with the Oral Glucose Tolerance Test. Rev. argent. endocrinol. metab. [online]. 2010, vol.47, n.4, pp.18-23. ISSN 1851-3034.

Introduction: IGF-I determination in serum or plasma is an essential tool in the diagnosis and follow-up of acromegaly. Hepatic production of IGF-I is regulated by GH and circulates bound to several IGF-I binding proteins which extends its half life. IGF-I is not released in a pulsatile pattern and has no significant variability in 24 h. Objective: To evaluate two different methodologies in IGF-I levels determination and their correlation with GH nadir in OGTT in acromegalic patients. Material and methods: We analyzed 37 acromegalic patients, 20 women and 17 men, mean age was 45±12 years. IGF-I levels were assayed by Immulite 1000, DPC (IMM) and DSL-5600 ACTIVE® IGF-I Coated-Tube IRMA (DSL) and OGTTs (at baseline and at 30, 60, 90 and 120 minutes) were performed by measuring plasma glucose and GH assay by immunochemiluminometric assay (Access); we considered a nadir <1ng/ml as normal response. Nine patients were under medical treatment (cabergoline: 4, octeotride: 4, and cabergoline plus octeotrite: 1) and 28 without treatment. Statistical analysis: Wilcoxon and, Bland and Altman tests and ROC curves. Differences were considered significant at p< 0.05. Results: Basal glucose levels were 97.86±10.91 mg/dl and mean GH was 2.8 (1.59-14.4) ng/ml. Mean IGF-I levels performed by IMM were 602±318 ng/ml and 1006±596 ng/ml by DSL. There was a statistically significant difference between both methodologies (p<0.01). Bland and Altman test showed a bias of - 403.2 ng/ml with lower values by IMM. We observed elevated IGF-I levels in 84% by IMM and in 97% by DSL, and only one patient had normal levels with both methodologies. Elevated IGF-I levels and GH nadir >1ng/ml were observed in 70% of the patients, increased IGF-I with normal GH nadir in 13.5%, normal IGF-I with GH nadir >1ng/ml in 2.7% and normal IGF-I with normal GH nadir in 13.5%. Patients under treatment: 3 showed normal GH nadir with elevated IGF-I levels, in 2 of them by both methodologies, and in the other one it was normal by IMM and elevated by DSL; the other 6 showed GH nadir > 1ng/ml, 5 of them presented elevated IGF-I by both methodologies and the other one showed discrepancy in IGF-I levels. The under ROC curve area and confidence interval (CI) of 95% for IGF-I IMM and DSL were 0.96 (0.90-1.00) and 0.91 (0.82-1.00) respectively. Differences between the ROC curves areas were not significant Conclusions: IGF-I levels determined by IMM and DSL were statistically significantly different. IGF-I levels showed a negative bias by IMM. Most of the results of GH nadir were consistent with IGF-I levels but we observed discrepancy in 30% of the patients, regardless of whether they were under treatment or not.

Keywords : Acromegaly; Immunoassay; OGTT.

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