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

Abstract

Objective we assessed the diagnostic accuracy of insulin-like growth factor 1 (IGF-1) measurements with one growth hormone stimulation test (GHST) versus performing two 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 two GHSTs. We compared the diagnostic values of IGF-1 levels by using a cutoff value of ≤ 0 standard deviation score (SDs), 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 two diagnostic methods. GHD was diagnosed if the peak growth hormone level was <7 ng/mL on two GHSTs. Results Of the 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-1cut-off level of ≤–2 SDs didn’t alter the diagnostic accuracy. Conclusions Low IGF-1 values of ≤0 SDs or ≤–2 SDs in combination with results of a single CST had poor diagnostic accuracy for GHD.