Using hypernatraemic events to predict reduced renal function in elderly lithium patients: a brief report

Background Diabetes insipidus ( DI ) is a recognized adverse effect of lithium use, and studies have shown an association between decreased renal function and DI in patients using lithium. We hypothesize that hypernatraemic events that occur in DI predict decreased renal function in elderly patients on lithium. Methods We conducted a retrospective cohort study involving 55 geriatric psychiatry patients using lithium between 1985 and 2010. Patients who always had sodium levels ≤146 mmol/ L were compared to patients with one or more episodes of hypernatraemia (serum sodium level ≥147 mmol/ L ) for estimated glomerular filtration rate ( eGFR ) levels and prevalence of severe chronic renal failure (eGFR ≤30  mL /min/1.73 m 2 ). Results eGFR was found to be less in the hypernatraemic group than in the non‐hypernatraemic controls (41 vs 56 mL/min/1.73 m 2 ; P = 0.0074). Severe chronic renal failure appeared more prevalent in hypernatraemic patients (4/14 (28.6%) vs. 3/41 (7.3%)), but this did not achieve statistical significance ( P = 0.061). The two groups did not differ for age, sex, medical comorbidities or other clinical variables, except antidepressant use. Hypernatraemic patients appeared less likely to use antidepressants than non‐hypernatraemic patients, odds ratio = 0.69 ( P = 0.020). However, in multivariate analysis, hypernatraemia correlated with decreased eGFR (β = −0.39, P = 0.004), while antidepressant use did not ( P = 0.81). Conclusions These results suggest that hypernatraemic events may predict reduced renal function in geriatric patients using lithium. The role of hypernatraemia and DI in renal failure in this population requires further study. Health professionals should be aware of the risks of renal failure in older patients treated with lithium, especially in the context of sodium level abnormalities.