[Clinical significance of urinary free dopamine as a marker of renal function]

Urinary free dopamine (DA) is derived from DA synthesized or converted from circulating DOPA in renal proximal tubules, and plays an important role for diuresis and natriuresis. As plasma free DA is in tiny amounts near detectable range, a large amount of free DA in urine is tubular origin, but not from circulating DA. In the present study, we hypothesized that urinary free dopamine (U-f-DA) can be used as the marker of renal function. We speculated that U-f-DA may decrease in the damage of renal tubules or renal disorder. To evaluate clinical significance of U-f-DA, we used serum creatinine levels as the index of renal function. As the urinary parameter of renal function, we measured U-f-DA, alpha(1)-microglobulin (U-alpha(1) MG), beta(2)-microglobulin (U-beta(2)MG) and N-acetyl-beta-D-glucosaminidase (U-NAG) in spot urine samples of 154 outpatients (male; 76, female; 78). Each values are rectified by creatinine (Cr) concentration in urine. U-f-DA was negatively correlated with the serum level of creatinine, U-alpha(1)MG and U-beta(2)MG. The receiver operating characteristic (ROC) curve analysis was used for their comparison in evaluation of urinary marker of renal function. In this analysis, area under the curve (AUC) of U-f-DA is best among other markers of renal function. AUC of U-f-DA/Cr, U-alpha(1)MG/Cr, U-beta(2)MG/Cr, U-NAG/Cr were 0.82, 0.57, 0.72, 0.62 in male, 0.92, 0.72, 0.81, 0.57 in female, respectively. These results suggest that the measurement of U-f-DA is superior marker of renal function to the determination of U-alpha(1)MG, U-beta(2)MG and U-NAG.