Impairment of renal function in patients on long-term lithium treatment

A survey of the renal function in 278 patients on long-term lithium treatment maintained on plasma lithium concentration of 0.7-1.2 mmoles/l was conducted. The extent of renal damage were studied with urinary concentration tests, beta-2-microglobulin excretion and measurement of glomerular filtration rate. The mean treatment time was 6.5 years and the longest treatment time was 15 years. Forty-nine per cent of the patients could not concentrate their urine to above 800 mOsm/kg of water, which did not correlate with the presence of polyuria. The urine concentration capacity decreased as a function of time in the lithium treated group, and it was also influenced by the type of tablet administration (readily soluble or sustained release), but not by combination with other drugs, such as neuroleptics. Beta-2-microglobulin excretion was not increased. A reduced glomerular filtration rate was found in 17% and the filtration rate in the whole group of patients was clustered around the lower limit of normal. The filtration rate decreased as a function of the duration of treatment. It was found that the concentrating capacity and the filtration rate decreased in parallel and that there was no selective impairment of the concentrating capacity. We conclude that severe impairment of renal function is uncommon in well controlled patients. Urinary concentration tests are shown to be the most suitable test for detection of kidney damage in long-term lithium treatment.