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 ��2-microglobulin (��2MG, 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/Vurea (eKt /Vurea) were calculated. The serum CyC concentrations were measured using particle-enhanced immunonephelometry. As indices of the middle molecular clearance, the reduction ratios of ��2MG and CyC were calculated. Results: The ��2MG reduction ratio (��2MGRR) 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/Vurea and ��2MGRR (r = 0.47 and 0.69, respectively, both p < 0.0001). Conclusions: Compared to the LF dialyzer, the HF dialyzer removed CyC and ��2MG more efficiently. Unlike the ��2MGRR, the CyCRR was correlated with the eKt/Vurea and ��2MGRR. This study suggests a role for the CyCRR as an alternative indicator of the removal of MMs