Determination of D-amino acids in serum from patients with renal dysfunction

D-Ala and D-Ser were detected in the sera of both normal subjects and patients with renal dysfunction, and their concentrations were higher in the patients than in the normal subjects. A positive correlation between the concentration of D-Ala or D-Ser and that of creatinine (r = 0.733, p < 0.001 or r = 0.634, p < 0.001) or blood urea nitrogen (BUN) (r = 0.449, p < 0.05 or r = 0.629, p < 0.001) was observed in sera from 20 patients with renal dysfunction. The fraction (%D) of D-Ala in the total Ala in serum ([D/(D+L)] x 100) correlated well with the concentration of creatinine (r = 0.811, p < 0.001), suggesting that it is a candidate as a marker for renal proximal tubular dysfunction. The correlations of %D of Ser with creatinine and BUN levels were 0.796 (p < 0.001) and 0.919 (p < 0.001), respectively, indicating that %D of Ser may reflect protein turnover or catabolism in certain tissues as well as renal proximal tubular dysfunction.