Dr. Dietzen's research is devoted to the assessment and improvement of existing clinical diagnostic tests and in exploiting novel biomarkers for pediatric disease. A particular focus is the development of metabolomic profiles using tandem mass spectrometry to assess inborn metabolic disease, hepatobiliary disease, disorders of iron metabolism, and primary mitochondrial disorders. He is involved in national efforts to define reference intervals and intraindividual variability in pediatric populations and continues work to improve the specificity and scope of clinical toxicology testing for pediatric clinical environments.