Clonidine Stimulation Test: Is Single Best Time Point, Convenient Yet Efficacious?

CONTEXT: To find a single time point during clonidine stimulation test (CST), with highest diagnostic value to rule out growth hormone deficiency (GHD). SETTINGS AND DESIGN: This is a retrospective study of 79 CSTs carried out in a tertiary care center in India. MATERIALS AND METHODS: A cohort of 79 children with unexplained short stature was divided into two groups: GHD and non-GHD. Any one stimulated growth hormone (GH) level >10 ng/mL was used to rule out GHD. Diagnostic accuracy of not only single time points but also time points in pairs was calculated. STATISTICAL ANALYSIS: The data were analyzed using SPSS statistical software 22.0. Descriptive statistics were used for analyzing demographic data. Mode for time to peak GH was calculated in each group. The specificity and false positive rates at each time point as well as combined time points were determined. RESULTS: Assaying a single sample at 60 min after clonidine resulted in 20.5% false positive tests with specificity of 79.5%. Addition of the 90 min sample increased specificity to 92.3%. CONCLUSION: The 60 min sample after clonidine stimulation was the best single sample to rule out GH deficiency. Combined sampling at 60 min + 90 min is economical and less cumbersome, with minimal compromise on the specificity.