EVIDENCE THAT UREA IS A BETTER SURROGATE MARKER OF UREMIC TOXICITY THAN CREATININE

The protein equivalent of nitrogen appearance normalized to standard w eight was determined from urea nitrogen appearance (nPNA U) and from t otal Kjeldahl nitrogen appearance (nPNA K) in dialysate and/or urine i n 45 predialysis patients (pre D) and in 95 patients on continuous amb ulatory peritoneal dialysis (CAPD). Correlations with weekly Kt/V-urea and creatinine clearance (C-cr, L/wk/1.73 m(2)) were determined; rena l contributions of Cc, in both populations were calculated both as tot al C-Cr (A) and as C-Cr by GFR (C-Cr [B], mean of renal C-Cr and C-ure a). Correlations with weekly Kt/V-urea were significant in individual (pre D: nPNA U 0.57, p < 0.01, and nPNA K 0.37, p < 0.01; CAPD: nPNA U 0.50, p < 0.01, and nPNA K 0.43, p < 0.01) and pooled populations (nP NA U 0.54, p < 0.01 and nPNA K 0.37, p < 0.01). Correlations with neit her C-cr (A) nor C-Cr (B) were significant. The data also allowed comm ent on mathematical coupling. C-cr vs nPNA K correlations share even m ore mathematical couplers than does the nPNA K vs Kt/V-urea correlatio n, yet the correlation of nPNA K with C-cr is quite low. The authors c onclude that urea is a better surrogate marker of small molecular weig ht toxins that inhibit protein intake in uremia, and correlations of n PNA with Kt/V-urea represent more than simple mathematical coupling.