Factors affecting serum and urinary guanidinosuccinic acid levels in normal and uremic subjects.

Guanidinosuccinic acid (GSA) was measured in serum and urine from six normal subjects, 26 chronically uremic patients, and 17 patients undergoing maintenance hemodialysis. All normal subjects and 22 chronically uremic patients were fed diets providing 21 gm of essential amino acids or 20, 40, or 60 gm/day of protein. Serum GSA was usually undetectable in normal subjects and was increased in uremic patients (0.99 +/- S.D. 044. mg/100 ml). Serum creatinine and urea nitrogen were each correlated with serum GSA in the normal and uremic subjects combined and in uremic patients alone. Serum GSA was greater in hemodialysis patients (1.43 +/- 0.56 mg/100 ml) than in uremic patients (p less than 0.02) and decreased by 39% +/- 21 during hemodialysis in five patients. Serum GSA and the serum GSA/creatinine ratio tended to decrease with low protein intake in the uremic patients. Urinary GSA was increased in uremic patients (30.5 +/- 12.9 mg/day) as compared to that in normal subjects (7.5 +/- 1.9 mg/day), was greater in uremic patients than in normal subjects at each level of protein intake, and was directly correlated with protein intake and urinary urea and total nitrogen in both normal and uremic subjects. In three uremic patients who developed intercurrent illnesses, urinary GSA rose transiently. These results indicate four factors which affect serum or urinary GSA levels: (1) renal function, (2) protein intake, (3) catabolic stress, and (4) hemodialysis therapy.