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 β(2)-microglobulin (β(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 β(2)MG and CyC were calculated. RESULTS: The β(2)MG reduction ratio (β(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 β(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 β(2)MG more efficiently. Unlike the β(2)MGRR, the CyCRR was correlated with the eKt/V(urea) and β(2)MGRR. This study suggests a role for the CyCRR as an alternative indicator of the removal of MMs.