Significance of insulin tolerance test in the diagnosis of adult growth hormone deficiency

Abstract

Objective To assess the significance of insulin tolerance test(ITT) in clinical diagnosis of adult growth hormone deficiency(GHD).Methods Eighty-two patients with an established diagnosis of adult GHD [53males,29 females,mean age (30.9 ± 12.3) years (18-65 years)] were reviewed retrospectively for evaluating the GH response to ITT in the General Hospital of the People' s Liberation Army.Control data for peak GH after ITT were obtained in 15 healthy subjects [9 males,6 females,mean age (26.7 ± 5.6) years (22-41 years)].Receiver operating characteristic (ROC) curve analysis and the area under the curve (AUC) were used to evaluate the diagnostic cut-off point of peak GH and GH increment response to ITT.Results (1) Mean peak GH response to ITT was significantly higher in 15 controls compared with 82 patients (the median 14 μg/L vs 0.62 μg/L,P =0.001).The cut-off point of the peak GH(chemiluminescent immunoassay,CLIA) response to ITT in adult GHD was 4.935 μg/L (AUC 0.993).(2) Mean GH increment was significantly higher in 15 controls compared with 82 patients (the median 13.17 μg/L vs 0.19 ug/L,P＜0.001).The cut-off point of the GH increment was 4.088 μg/L(AUC 0.937),with a 91.5％ sensitivity and 100％ specificity.(3) The peak GH showed even higher diagnostic value than the GH increment after ITT.(4)The above mentioned cut-off points (peak GH less than 4.935 μg/L and 5 μg/L) had a coincidence with a 95.1％ sensitivity and 100％ specificity,respectively.Conclusion The current guidelines for the diagnosis of adult GHD based on the optimal cut-off point of the peak GH(CLIA) response to ITT less than 5 μg/L turned to be of reliable diagnostic value in our country. Key words: Insulin tolerance test; Cut-off point; Adult growth hormone deficiency; Growth hormone