Low IGF-1 SDS ≤ -2.5 combined with single clonidine test achieves 98.6% specificity for pediatric GHD diagnosis.
Background
Diagnosing Growth Hormone Deficiency (GHD) in children is challenging due to the pulsatile nature of GH secretion, necessitating dynamic stimulation tests. While the clonidine test is a standard, current guidelines often require two such tests for confirmation, increasing patient burden and healthcare costs. Insulin-like growth factor-1 (IGF-1), a GH-dependent biomarker, offers potential as an adjunct, but its standalone diagnostic accuracy is limited. This study addresses the diagnostic gap by evaluating the effectiveness of combining low IGF-1 levels with a single clonidine test to improve diagnostic confidence and potentially streamline the GHD evaluation process.
Study Design
A retrospective cohort study was conducted at King Chulalongkorn Memorial Hospital, analyzing data from 214 children with short stature, aged 2-16 years, evaluated between August 2019 and January 2025. GHD was confirmed in 63 patients based on two GH stimulation tests, with a peak GH level of <7 ng/mL>. Serum IGF-1 levels were expressed as standard deviation scores (SDS) and assessed at various cutoff points, including ≤ -1, -1.5, -2, -2.5, and ≤ -3. These IGF-1 SDS cutoffs were then combined with the results of a single clonidine test. The primary endpoints were the calculated sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) for each combination.
Results
The combination of IGF-1 SDS ≤ -2.5 and a single clonidine test (peak GH <7 ng/mL>) demonstrated robust diagnostic performance, particularly in specificity. This specific combination yielded a sensitivity of 31.6% and a high specificity of 98.6%. The positive predictive value (PPV) was 92.3%, indicating a high likelihood of GHD when both criteria are met, while the negative predictive value (NPV) was 73.7%. These findings suggest that a positive result from this combined approach strongly indicates GHD. Additionally, exploring a less stringent IGF-1 SDS cutoff of ≤ -1.5 in combination with a single clonidine test resulted in an improved sensitivity of 60.5% and a still high specificity of 95.9%. This indicates a trade-off between sensitivity and specificity based on the chosen IGF-1 threshold. The high specificity observed with the ≤ -2.5 cutoff is particularly noteworthy:
The combination of IGF-1 SDS ≤ -2.5 and a single clonidine test (peak GH <7 ng/mL) demonstrated a sensitivity of 31.6% and a specificity of 98.6%.
Key Findings
- Combination of IGF-1 SDS ≤ -2.5 and single clonidine test showed 98.6% specificity for GHD.
- This combination yielded a positive predictive value (PPV) of 92.3%.
- Sensitivity for IGF-1 SDS ≤ -2.5 with single clonidine test was 31.6%.
- An IGF-1 SDS ≤ -1.5 cutoff improved sensitivity to 60.5% while maintaining 95.9% specificity.
Why It Matters
This study offers a practical advancement for diagnosing pediatric Growth Hormone Deficiency (GHD), potentially reducing the need for multiple, burdensome stimulation tests. For clinicians, combining a low IGF-1 SDS (specifically ≤ -2.5) with a single failed clonidine test can provide high diagnostic confidence, particularly in ruling in GHD, given the 98.6% specificity. This could translate to fewer hospital visits and reduced stress for children and families undergoing evaluation. While not replacing the need for a second test entirely in all cases, this approach could identify a subset of patients where a single test, augmented by IGF-1 data, is sufficient for a confident diagnosis. This could streamline diagnostic protocols, making the process more efficient and patient-friendly, especially in resource-constrained settings.
growth-hormone-deficiency
ghd
igf-1
clonidine
pediatric
diagnosis