Renal Clearance of Intravenously Administered Vitamin B12

Abstract
At plasma levels ranging from 0.3 to 1.5 [mu]g/ml the urinary excretion of B12 is a function of the degree of B12 binding by plasma protein. At constant plasma levels between 12 and 26 [mu]g/ml of vitamin B12, the urinary excretion of B12 in a given individual is proportional to plasma level and glomerular filtration rate. No relation of renal clearance of B12 with advancing age was noted except for that resulting from the gradual reduction in glomerular filtration rate with age.