Urinary guanidinoacetate-guanidinosuccinate ratio: an indicator of kidney dysfunction.

Five formerly unidentified peaks in the column chromatogram of urinary compounds giving the Sakaguchi reaction appear to be proteins or polypeptides containing arginine. If these substances, salts, and creatine are first removed, then guanidinoacetate (GAA), guanidinosuccinate (GSA), and creatine are readily measured in urine. This technique was applied to the urine of 17 healthy men and 10 healthy women, GAA and GSA being measured by the Sakaguchi reaction (after they were separated by electrophoresis) and creatine by the diacetyl reaction. Creatine and GAA values differ for men and women when corrected for differences in body weight. In mg/24 h/kg body weight, the respective excretions for men and women were: creatine, 0.83 and 1.98; GAA, 0.71 and 1.22. No significant sex-related differences were found for GSA (men, 0.18; women, 0.25) or creatinine (men, 24.7; women, 22.8). The GSA/GAA excretion ratio for healthy men and women was 0.25 and 0.20, respectively. For those with abnormally high blood urea nitrogen and creatinine concentrations, this ratio rose to values ranging from 1.8 to 24, with no overlap with normal. This ratio is evidently a sensitive indicator of kidney function.