This study aims to establish normal values of cortisol and ACTH after overnight dexamethasone suppression in children and adolescents aged 5 to 18 years. Cushing syndrome is rare in this age group and diagnosis is difficult because children often present with growth failure with weight gain rather than typical adult features. Current biochemical tests include overnight dexamethasone suppression test low dose dexamethasone suppression test and 24 hour urinary free cortisol. However pediatric specific reference values especially using modern testing methods are limited.

This prospective study will enroll 120 healthy participants attending endocrine or community medicine outpatient services. Eligible participants will undergo clinical evaluation and anthropometry. Dexamethasone will be given at a dose of 15 microgram per kilogram body weight with maximum 1 mg at 11 PM. Blood samples will be collected next morning at 8 to 9 AM for cortisol ACTH thyroid profile renal and liver function hemoglobin and serum dexamethasone level. Participants with cortisol above 1.8 microgram per deciliter will undergo further evaluation.

Hormone levels will be measured using chemiluminescent assays and dexamethasone levels by LCMS. Statistical analysis will compare quantitative and categorical variables with significance level of 0.05.The results aim to provide reliable pediatric reference cutoffs to improve diagnosis of Cushing syndrome.