Screening for hypothalamic–pituitary–adrenal axis suppression in asthmatic children remains problematic: a cross-sectional study

OBJECTIVE: To determine which parameter is the most useful screening test for hypothalamic–pituitary–adrenal suppression in asthmatic children. DESIGN: Cross-sectional study. SETTING: Paediatric allergy clinics in Cape Town, South Africa. PARTICIPANTS: 143 asthmatic children of mostly mixed ancestry, aged 5–12 years. OUTCOME MEASURES: Primary outcome measures included Spearman correlation coefficients (r) calculated between the postmetyrapone (PMTP) serum adrenocorticotropic hormone (ACTH), 11-deoxycortisol (11DOC), 11DOC+ cortisol (C) and height, weight, height velocity, weight velocity, change in systolic blood pressure from supine to standing, early morning urinary free cortisol (UFC), morning C, ACTH and dehydroepiandrosterone sulfate (DHEAS). Secondary outcome measures were the receiver operating characteristics (ROC) curve and the diagnostic statistics for the most promising test. RESULTS: All screening variables were weakly correlated with the three PMTP outcomes. Only DHEAS and UFC (nmol/m(2)) were statistically significant—DHEAS for PMTP ACTH and 11DOC (r=0.20, p=0.025 and r=0.21, p=0.017); UFC (nmol/m(2)) for PMTP 11DOC and 11DOC+C (r=0.19, p=0.033 and r=0.20, p=0.022). The area under ROC curve for DHEAS in the 5-year to 9-year age group was 0.69 (95% CI 0.47 to 0.92). At DHEAS cut-off of 0.2 µmol/L: sensitivity=0.88 (CI 0.47 to 1.00), specificity=0.61 (CI 0.42 to 0.78), positive predictive value=0.37 (CI 0.16 to 0.62), negative predictive value=0.95 (CI 0.75 to 1.00), accuracy=0.67 (CI 0.50 to 0.81), positive likelihood ratio=2.26 (CI 1.35 to 3.78), negative likelihood ratio=0.20 (CI 0.03 to 1.30). CONCLUSIONS: No parameter is useful as a universal screening test. DHEAS may be suitable to exclude HPAS before adrenarche. Further research is needed to confirm these findings and identify factors, for example, genetic that may predict or protect against HPAS.