Background/Aims: In pre-dilution hemofiltration (HF), solute clearance is less than the HF rate. While the amount of this loss is predictable, it has not been validated in high-volume HF associated with high blood flow rates. Methods: Using isovolemic pre-dilution HF, we studied small solute clearances using combinations of blood flow (QB; 150, 250, 350, 450 ml/min) and replacement fluid (RF) flow (QRF; 2, 4, 6 l/h) to determine clearance losses we entitled ‘measured efficiency’ (EM). EM was compared to predicted efficiency (EP) = (QB/QB + QRF). Results: Pre-dilution produced EM values of 61–93%. Increases in QB for any QRF and decreases in QRF for any QB increased EM over a wide range of QB and QRF. EP was equivalent to EM. Conclusion: In high-volume pre-dilution HF, EP can be used to determine EM across a broad range of QB and QRF values. Higher QRF requires higher QB to minimize the attenuating effects of pre-dilution on clearance.

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