Paediatric reference range for overnight urinary cortisol corrected for creatinine.

OBJECTIVES Systemic activity of inhaled corticosteroids (ICS) may be assessed via urinary cortisol measurement. Overnight urinary free cortisol corrected for creatinine (OUFCC) has been extensively reported in adult studies. However, a paediatric mass spectrometric (MS) reference range for OUFCC is not established. MS methods for OUFCC avoid cross-reactivity with other steroid hormones and are thus preferable to immunoassays. The aim of the present study was to define an MS OUFCC normative range in children. METHODS This was a cross-sectional study of healthy pre-pubertal children from 5 to 11 years. Children collected urine from 10 pm or bedtime, whichever was earlier, until 8 am. Urinary free cortisol was measured via a liquid chromatography tandem mass spectrometry (LC-MS/MS) assay (Acquity UPLC with Xevo TQ-S Mass Spectrometer [Waters]) with in-house reagents. Urinary creatinine was measured using a commercial assay (Roche). RESULTS Complete urine collections were obtained from 72 males and 70 females, mean age (SD) 8.6 (1.9) (range 5.0-11.8) years. The OUFCC 95% prediction interval was 1.7-19.8 nmol/mmol. Geometric mean OUFCC was 5.7; range 1.1-24.8 nmol/mmol. CONCLUSIONS The obtained normative LC-MS/MS OUFCC reference data facilitate the use of mass spectrometry OUFCC assays in assessment of systemic activity of endogenous and exogenous corticosteroids in children.