The use of lithium clearance measurements as an estimate of glomerulo-tubular function

Lithium clearance measurements are based on the observation that lithium un dergoes isoosmotic reabsorption in the proximal renal tubule to the same ex tent as salt and water, but undergoes neither reabsorption nor secretion el sewhere in the nephron. Consequently, lithium clearance values estimate the delivery of isoosmotic fluid to the loop of Henle and hence provide an ass essment of proximal tubular reabsorption of isoosmotic fluid. If sodium cle arance and urinary flow rate are also measured, then this allows the deriva tion of a number of parameters relating to both the absolute and relative r enal handling of isoosmotic fluid in the proximal and distal regions of the kidney. Consequently, lithium clearance techniques can be used in both exp erimental and clinical studies to evaluate glomerulo-tubular function and p rovide information regarding the handling of sodium and water by the proxim al and distal nephron in both health and disease. The use of lithium cleara nce measurements in the assessment of glomerulo-tubular function in patient s treated with rIL2 for colorectal cancer is described and its application to both drug-induced toxicity and other disease states discussed.