Measurement of reference intervals for urinary free adrenal steroid levels in Japanese newborn infants by using stable isotope dilution gas chromatography/mass spectrometry

► We established a method for simultaneous measuring of 9 urinary free adrenal steroids. ► We validated this GC/MS method and demonstrated good accuracy and precision. ► We determined reference intervals of 9 urinary free steroids in newborn infants. ► They may help elucidate the dynamics of urinary free adrenal steroids.