Discordant GH and IGF-1 Results in Treated Acromegaly: Impact of GH Cutoffs and Mean Values Assessment

CONTEXT: Discordant growth hormone (GH) and insulin-like growth factor-1 (IGF-1) values are frequent in acromegaly.OBJECTIVE: To evaluate the impact of different GH cutoffs on discordance rate. To investigate whether the mean of consecutive GH measurements impacts discordance rate when matched to the last available IGF-1 value.DESIGN: Retrospective study.SETTING: Referral center for pituitary diseases.PATIENTS: Ninety acromegaly patients with at least 3 consecutive evaluations for GH and IGF-1 using the same assay in the same laboratory (median follow-up 13 years).INTERVENTIONS: Multimodal treatment of acromegaly.MAIN OUTCOME MEASURES: Single fasting GH (GHf) and IGF-1 (IGF-1f). Mean of 3 GH measurements (GHm), collected during consecutive routine patients' evaluations.RESULTS: At last evaluation GHf values were 1.99 ± 2.79 g/L and age-adjusted IGF-1f was 0.86 ± 0.44 * upper limit of normality (mean ± SD). The discordance rate using GHf was 52.2% (cutoff 1 g/L) and 35.6% (cutoff 2.5 g/L) (P = 0.025). "High GH" discordance was more common for GHf <1.0 g/L, while "high IGF-1" was predominant for GHf <2.5 g/L (P < 0.0001). Using GHm mitigated the impact of GH cutoffs on discordance (GHm <1.0 g/L: 43.3%; GHm <2.5 g/L: 38.9%; P = 0.265). At receiver-operator characteristic curve (ROC) analysis, both GHf and GHm were poor predictors of IGF-1f normalization (area under the curve [AUC] = 0.611 and AUC = 0.645, respectively). The prevalence of disease-related comorbidities did not significantly differ between controlled, discordant, and active disease patients.DISCUSSION: GH/IGF-1 discordance strongly depends on GH cutoffs. The use of GHm lessen the impact of GH cutoffs. Measurement of fasting GH levels (both GHf and GHm) is a poor predictor of IGF-1f normalization in our cohort.