Lack of concordance in defining worsening renal function by rise in creatinine vs rise in cystatin C.

Worsening renal function (WRF) during treatment of acute decompensated heart failure (ADHF) is generally associated with adverse outcomes. An increase ≥0.3 mg/dL in creatinine level is widely used as the definition of WRF. The authors sought to determine the level of agreement between WRF based on changes in creatinine and changes in cystatin C (CysC) by analyzing data from 121 ADHF patients with available admission and day 3 creatinine and CysC levels. Admission creatinine and CysC levels were 1.39 (0.98-2.11) mg/dL and 1.95 (1.42-2.69) mg/L, respectively, and correlated well (r=0.81). On average, creatinine (-0.04±0.40 mg/dL) and CysC (0.001±0.34 mg/L) changed minimally from admission to day 3. Although the correlation between both markers on day 3 was still good (r=0.79), the correlation between changes therein was only modest (r=0.43). From the 14 and 15 patients who had WRF based on a ≥0.3 mg/dL increase in creatinine and ≥0.3 mg/L increase in CysC, respectively, only four (about 30%) met both definitions. These observations, together with recent insights in the inconsistencies of creatinine-defined concept of worsening renal function and outcomes, raises the need to research more reliable measures of renal function during treatment of ADHF.