The renal lithium clearance and its correlations with other biological variables: observations in a large group of physically healthy persons.

The lithium clearance (CLi) is a measure of the delivery of fluid from the proximal tubules to the loop of Henle. We determined the correlations between CLi and a number of variables on 350 occasions in 164 physically healthy persons in lithium treatment for manic-depressive illness. CLi was significantly correlated (p less than 0.001) with sex, age, body surface, urine flow, sodium clearance, potassium clearance, serum lithium concentration, and lithium dosage. Correlations with sex, age and body surface lost statistical significance when the renal variables and the surface were divided by creatinine clearance; these correlations are indirect and caused by common correlations with the filtration rate. The findings show that the fractional delivery of fluid from the proximal tubules is independent of sex, age and body surface. Correlations with urine flow, serum lithium, and lithium dosage could be explained by circumstances connected with the lithium treatment. These variables do not seem to affect CLi. It is concluded that factors which should be taken into account if the assessment of lithium clearance values include the creatinine clearance, the sodium clearance, and the potassium clearance.