Application of Cystatin C Reduction Ratio to High-Flux Hemodialysis as an Alternative Indicator of the Clearance of Middle Molecules

BACKGROUND/AIMS Although high-flux (HF) dialyzers with enhanced membrane permeability are widely used in current hemodialysis (HD) practice, urea kinetic modeling is still being applied to indicate the adequacy of both low-flux (LF) and HF HD. In comparison with urea (molecular weight, 60 Da) and beta(2)-microglobulin (beta(2)MG, 12 kDa), cystatin C (CyC, 13 kDa) is a larger molecule that has attractive features as a marker for assessing solute clearance. We postulated that CyC might be an alternative for indicating the clearance of middle molecules (MMs), especially with HF HD. METHODS Eighty-nine patients were divided into LF and HF groups. Using single pool urea kinetic modeling, the urea reduction ratio (URR) and equilibrated Kt/V(urea) (eKt/V(urea)) were calculated. The serum CyC concentrations were measured using particle-enhanced immunonephelometry. As indices of the middle molecular clearance, the reduction ratios of beta(2)MG and CyC were calculated. RESULTS The beta(2)MG reduction ratio (beta(2)MGRR) and CyC reduction ratio (CyCRR) were higher in the HF group compared to the LF group. However, the URR and eKt/Vurea did not differ between the two groups. The CyCRR was significantly correlated with the eKt/V(urea) and beta(2)MGRR (r = 0.47 and 0.69, respectively, both p < 0.0001). CONCLUSIONS Compared to the LF dialyzer, the HF dialyzer removed CyC and beta(2)MG more efficiently. Unlike the beta(2)MGRR, the CyCRR was correlated with the eKt/V(urea) and beta(2)MGRR. This study suggests a role for the CyCRR as an alternative indicator of the removal of MMs.