Diagnostic Value of IGF-1 in Growth Hormone-Deficient Children: Is a Second Growth Hormone Stimulation Test Necessary?

Objective: we assessed the diagnostic accuracy of insulin-like growth factor (IGF) 1 measurements with 1 growth hormone stimulation test (GHST) vs performing 2 GHSTs as the standard test to confirm the diagnosis of growth hormone deficiency (GHD) in children. Methods: We retrospectively analyzed the baseline characteristics, anthropometric measurements, and laboratory data of 703 children with short stature, aged 4-14 years (mean age, 8.46 ± 2.7 years), who had undergone 2 GHSTs. We compared the diagnostic values of IGF-1 levels by using a cut-off value of ≤0 SD score, along with results of a single clonidine stimulation test (CST). We evaluated the false-positive rate, specificity, likelihood ratio, and area under the curve (AUC) of the 2 diagnostic methods. GHD was diagnosed if the peak growth hormone level was <7 ng/mL on 2 GHSTs. Results: Of the 724 children, 577 (79.7%) had a low IGF-1 level (mean 104.9 ± 61.4 ng/mL), and 147 (20.3%) had a normal IGF-1 level (mean 145.9 ± 86.9 ng/mL). GHD was diagnosed in 187 patients (25.8%), of whom 146 (25.3%) had a low IGF-1 level. An IGF-1 level reflecting ≤0 SDs in combination with results of a single CST had a specificity of 92.6%, a false-positive rate of 5.5%, and an AUC of 0.6088. Using an IFG-1 cut-off level of ≤-2 SDs did not alter the diagnostic accuracy. Conclusion: Low IGF-1 values of ≤0 SDs or ≤-2 SDs in combination with results of a single CST had poor diagnostic accuracy for GHD.