Peak Growth Hormone Response to Combined Stimulation Test in 315 Children and Correlations with Metabolic Parameters

Background/Aims: Studies are lacking regarding the timing of peak growth hormone (PGH) response. We aim to elucidate the timing of PGH response to arginine and levodopa (A-LD) and evaluate the influence of body mass index (BMI) and other metabolic parameters on PGH. Methods: During growth hormone (GH) stimulation testing (ST) with A-LD, serum GH was measured at baseline and every 30 min up to 180 min. The PGH cut-off was defined as <10 ng/mL. IGF-1, IGF BP3, BMI, and metabolic parameters were obtained in a fasting state at baseline. Results: In the 315 tested children, stimulated PGH levels occurred at or before 120 min in 97.8% and at 180 min in 2.2%. GH area under the curve (AUC) positively correlated with PGH in all patients and with IGF-1 in pubertal males and females. BMI negatively correlated with PGH in all subjects. GH AUC negatively correlated with HOMA-IR and total cholesterol. Conclusion: We propose termination of the GH ST with A-LD at 120 min since omission of GH measurement at 180 min did not alter the diagnosis of GH deficiency based on a cut-off of < 10 ng/mL. BMI should be considered in the interpretation of GH ST with A-LD. The relationships between GH AUC and metabolic parameters need further study.