Fatih Kilci, Emre Sarıkaya
Trends in Pediatrics - 2025;6(4):253-259
Background: Growth hormone deficiency (GHD) is a significant cause of growth failure in children and is diagnosed through growth hormone (GH) stimulation tests. However, the sensitivity and specificity of these tests vary, leading to different protocols across centers. Clonidine and Levodopa (L-DOPA) are two commonly used GH-stimulating agents in pediatric endocrinology, yet data on their diagnostic performance and comparative effectiveness remain limited. This study aimed to evaluate the results of L-DOPA and clonidine stimulation tests in patients undergoing evaluation for suspected GHD at our clinic. Methods: A retrospective analysis was conducted on patients who underwent both L-DOPA and clonidine stimulation tests between January 2020 and January 2025. Demographic, anthropometric, and biochemical parameters, including Insulin-like growth factor-1 (IGF-1) and Insulin-like growth factor-binding protein-3 (IGFBP-3) levels, were recorded. Tests were performed after an overnight fast, with oral administration of L-DOPA (10 mg/kg) and clonidine (150 mg/m²) at 08:00-09:00 AM, followed by GH measurements at 0, 30, 60, 90, and 120 minutes. A peak GH level <7 ng/mL in both tests was used to define GHD. Results: A total of 133 patients (median age: 10 years, range: 1.3-16.1; 62.4% male) were included. There were 67 patients diagnosed with GHD and 66 patients without GHD. The median peak GH response was significantly higher with clonidine (6.9 ng/mL) than with L-DOPA (3.2 ng/mL) (p<0.001). In 95.5% of cases, the L-DOPA test yielded lower peak GH responses than the clonidine test. There were no significant differences between the GHD and non-GHD groups in terms of age, sex, height standard deviations (SD), body mass index (BMI) SD, or IGF-1 SD. However, the GHD group had a significantly higher proportion of pubertal cases, along with significantly lower IGFBP-3 SD levels and peak GH responses on both the L-DOPA and clonidine tests compared to the non-GHD group. IGFBP-3 SD showed a weak positive correlation with peak GH responses in both the L-DOPA (r=0.261, p=0.044) and clonidine (r=0.294, p=0.033) tests in the GHD group. Additionally, in the GHD group, a weak negative correlation was observed between BMI SD and peak GH responses in the clonidine test (r = -0.279, p = 0.032), whereas no correlation was observed between BMI SD and peak GH responses in the L-DOPA test (p = 0.358). Conclusions: Our findings indicate that clonidine stimulation results in significantly higher GH peaks compared to L-DOPA and demonstrates greater specificity. Using clonidine as the first-line stimulation test may reduce the number of unnecessary tests and associated costs in the diagnostic process. Furthermore, IGFBP-3 levels appeared to be more closely associated with GHD than IGF-1 levels, suggesting that IGFBP-3 could serve as an additional diagnostic marker. Larger-scale studies are warranted to validate these findings and optimize GHD screening strategies.
