The difference between cystatin C- and creatinine-based assessment of kidney function in acute heart failure

Aims Acute heart failure (HF) is associated with muscle mass loss, potentially leading to overestimation of kidney function using serum creatinine-based estimated glomerular filtration rate (eGFR(sCr)). Cystatin C-based eGFR (eGFR(CysC)) is less muscle mass dependent. Changes in the difference between eGFR(CysC) and eGFR(sCr) may reflect muscle mass loss. We investigated the difference between eGFR(CysC) and eGFR(sCr) and its association with clinical outcomes in acute HF patients. Methods and results A post hoc analysis was performed in 841 patients enrolled in three trials: Diuretic Optimization Strategy Evaluation (DOSE), Renal Optimization Strategies Evaluation (ROSE), and Cardiorenal Rescue Study in Acute Decompensated Heart Failure (CARRESS-HF). Intra-individual differences between eGFRs (eGFR(diff)) were calculated as eGFR(CysC)-eGFR(sCr) at serial time points during HF admission. We investigated associations of (i) change in eGFR(diff) between baseline and day 3 or 4 with readmission-free survival up to day 60; (ii) index hospitalization length of stay (LOS) and readmission with eGFR(diff) at day 60. eGFR(CysC) reclassified 40% of samples to more advanced kidney dysfunction. Median eGFR(diff) was -4 [-11 to 1.5] mL/min/1.73 m(2) at baseline, became more negative during admission and remained significantly different at day 60. The change in eGFR(diff) between baseline and day 3 or 4 was associated with readmission-free survival (adjusted hazard ratio per standard deviation decrease in eGFR(diff): 1.14, P = 0.035). Longer index hospitalization LOS and readmission were associated with more negative eGFR(diff) at day 60 (both P <= 0.026 in adjusted models). Conclusions In acute HF, a marked difference between eGFR(CysC) and eGFR(sCr) is present at baseline, becomes more pronounced during hospitalization, and is sustained at 60 day follow-up. The change in eGFR(diff) during HF admission and eGFR(diff) at day 60 are associated with clinical outcomes.