Title: Micronutrient and amino acid losses during renal replacement therapy for acute kidney injury.

Introduction: Malnutrition is common in patients with acute kidney injury (AKI), particularly in those requiring renal replacement therapy (RRT). Use of RRT removes metabolic waste products and toxins, but it will inevitably also remove useful molecules such as micronutrients, which might aggravate malnutrition. The RRT modalities vary in mechanism of solute removal; for example, intermittent hemodialysis (IHD) uses diffusion, continuous veno-venous hemofiltration (CVVH) uses convection, and sustained low-efficiency diafiltration (SLEDf) uses a combination of these. Methods: We assessed micronutrient and amino acid losses in 3 different RRT modalities in patients with AKI (IHD, n = 27; SLEDf, n = 12; CVVH, n = 21) after correction for dialysis dose and plasma concentrations. Results: Total losses were affected by modality; generally CVVH >> SLEDf > IHD (e.g., amino acid loss was 18.69 +/- 3.04, 8.21 +/- 4.07, and 5.13 +/- 3.1 g, respectively; P < 0.001). Loss of specific trace elements (e.g., copper and zinc) during RRT was marked, with considerable heterogeneity between RRT types (e.g., +849 and +2325 mu g/l lost during SLEDf vs. IHD, respectively), whereas effluent losses of copper and zinc decreased during CVVH (effect size relative to IHD, -3167 and -1442 mu g/l, respectively). B vitamins were undetectable in effluent, but experimental modeling estimated 40% to 60% loss within the first 15 minutes of RRT. Conclusion: Micronutrient and amino acid losses are marked during RRT in patients with AKI, with variation between RRT modalities and micronutrients.