Urinary reference ranges and exposure profile for lithium among an Italian paediatric population

Highlights: • Urinary Li reference range of Italian children is 3.8–51.9 μg L^{− 1} for evening samples. • Urinary Li reference range of Italian children is 4.8–71.7 μg L^{− 1} for morning samples. • Age and urinary Li levels are inversely correlated in evening and morning samples. • Urinary creatinine and Li levels are directly related in evening and morning samples. The aims of the present study were to establish reference values useful in monitoring Lithium (Li) treatment and to trace environmental Li exposure profiles in paediatric age. A cross-sectional study was conducted on a group of healthy Italian children aged 5–11. Data on possible predictors were assessed through a questionnaire, and Li levels in morning and evening urinary samples were determined by ICP-MS technique. The reference intervals for the evening and morning samples were respectively 3.8–51.9 μg L^{− 1} or 5.6–60.6 μg g^{− 1} creatinine and 4.8–71.7 μg L^{− 1} or 4.8–73.2 μg g^{− 1} creatinine. Urinary Li levels showed a significantly inverse correlation with age and a positive correlation with urinary creatinine in both the evening and morning samples. No other studied variables influenced Li urinary excretion. These results, obtained using a readily available matrix as urine, can be useful for both environmental research and Li treatment monitoring.