The Effect of Serum Lithium Levels on Renal Function in Geriatric Outpatients: A Retrospective Longitudinal Study

Abstract

Lithium remains an important treatment for bipolar disorder; however, whether elevated lithium levels lead to long-term renal problems is unknown. Previous consensus opinion was that levels should be kept below 0.6 mmol/L in geriatric patients to minimize renal toxicity. We hypothesized that elevated serum lithium levels correlate with decreased renal function [estimated glomerular filtration rate (eGFR)] in geriatric psychiatry outpatients. This was a 4-year retrospective cohort study (2007-2011). We performed this study in three Canadian university-affiliated tertiary care clinics. Data from 42 lithium-using geriatric psychiatry outpatients was used. INTERVENTION/EXPOSURE: Our main exposure of interest was mean serum lithium level between 2007 and 2011. Our primary outcome was change in eGFR between 2007 and 2011 (hypothesis formulated before data collection). Lithium levels did not correlate significantly with change in eGFR at 2- or 4-year follow-up (r < 0.12, p > 0.57). There were no significant predictors of change in eGFR in a multiple linear regression model including hypertension, diabetes, baseline eGFR, lithium duration, and lithium levels. Lithium levels do not correlate strongly (ρ > 0.5) with decreased eGFR at 2- and 4-year follow-up in geriatric outpatients. These results are not reliably generalizable when treating patients at mean lithium levels greater than 0.8 mEq/L, especially at 4-year follow-up, and larger studies will be necessary to examine the possibility of a smaller correlation. Nonetheless, these data and the existing literature suggest that lithium levels up to 0.8 mmol/L are safe for use in the long-term treatment of geriatric patients with mood disorders without pre-existing chronic renal failure.