Protein losses in continuous renal replacement therapies

Continuous renal replacement therapy (CRRT) has become a popular treatment modality but may have the disadvantage of producing substantial protein losses. With use of the Biuret method, a relatively insensitive assay, dialysate/ultrafiltrate protein losses have been reported to be as high as 1.3 g/L. With CRRT outputs of up to 50 L/day, these values would amount to protein losses of up to 65 g/day. In this study, dialysate/ultrafiltrate protein losses were reanalyzed by using a highly sensitive microprotein reagent (pyrogallol red) considered to be more accurate than previously available methods. Twenty-two dialysate/ultrafiltrate samples were obtained from Amicon-20 Diafilters or Fresenius F-80 dialyzers during continuous venovenous hemofiltration (CVVH) or continuous venovenous hemodialysis/hemodiafiltration (CVVHD/F). Mean hourly output for all treatments was 1637 ± 694 mL/h. Mean protein concentration for all 22 dialysate/ultrafiltrate samples was 4.2 ± 4.0 mg/dL. Mean dialysate/ultrafiltrate protein concentrations were similar for the Amicon 20 (3.4 ± 4.4 mg/dL, N = 9) and the Fresenius F-80 (4.7 ± 3.9 mg/dL, N = 13) (P = not significant). Protein losses were higher during convection-based CVVH (6.0 ± 5.1 mg/dL, N = 10; range, 1 to 15 mg/dL) than during the mixed convection and diffusion-based CVVHD/F (2.7 ± 1.9 mg/dL, N = 12; range, 0 to 6 mg/dL) (P = 0.049). Mean serum protein concentration at the time of dialysate/ultrafiltrate sampling was 4.7 ± 1.8 g/dL. There was a weak, but statistically significant correlation between the dialysate/ultrafiltrate samples and the corresponding value for serum protein (r = 0,468, P < 0.03). It was concluded that protein losses during CRRT treatments are substantially lower than previously reported, are dependent on the serum protein concentration and the predominant nature of solute removal (convection versus diffusion), and can vary between 1.2 and 7.5 g/day.