The United States of America As Represented by the Secretary of

Peter L Choyke

Joseph A Frank

Howard A Austin

A method of determining the glomerular filtration rate of a subject comprises (1) obtaining a serum sample S.sub.pre and a urine sample U.sub.pre from a subject; (2) administering to the subject an amount of a paramagnetic substance that is filtered by the kidneys and is readily detectable by NMR in serum and urine; (3) allowing for the concentration of the substance to equilibrate between the blood and the extravascular spaces; (4) separating an aliquot of the urine sample v.sub.A and obtaining a serum sample from the subject at the time t.sub.A ; (5) calculating a urine rate (v/a).sub.A from the formula (v/a).sub.A =V.sub.A /a.sub.A ; (6) measuring the magnetic resonance relaxation times of the serum and urine samples, (7) obtaining the concentrations of the paramagnetic substance in the serum samples and the urine samples by comparing their relaxation times to a standard; and (8) calculating GFR from the formula ##EQU1##

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Bethesda, MD, United States of America

Peter L Choyke