Kidney function estimates using cystatin C versus creatinine: Impact on medication prescribing in acutely...

Medication errors due to inaccurate measures of kidney function are common among elderly patients. We investigated differences between estimated glomerular filtration rate (eGFR) based on creatinine and cystatin C and how these differences would affect prescribing recommendations among acutely hospitalized elderly patients. We also identified factors associated with discrepancies between estimates.

Estimated glomerular filtration rate and chronic kidney disease (CKD) classifications were determined for 338 acutely hospitalized elderly patients using equations from Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI), Berlin Initiative Study (BIS) and Cockcroft-Gault (CG). Prescribed renal risk medications were compared with dosing guidelines in Renbase^® . Linear regression models were used to identify explanatory variables for eGFR discrepancies between equations. Muscle weakness was assessed by handgrip strength; inflammation was assessed by smoking status, serum C-reactive protein (CRP), soluble urokinase plasminogen activator receptor (suPAR) and neutrophil gelatinase-associated lipocalin (NGAL); and organ dysfunction was assessed by thyroid-stimulating hormone (TSH) and FI-OutRef.

Median eGFR values were 65.5, 60.7, 54.1, 57.1, 55.1 and 57.6 mL/min/1.73m² according to CKD-EPI_Cr , CKD-EPI_Comb , CKD-EPI_Cys , BIS_Cr , BIS_Comb and CG_Cr , respectively. Depending on choice of equation, renal risk medications were prescribed at higher than recommended dose in 13.6% to 22.5% of patients using normalized GFR units and 9.9% to 19.1% of patients using absolute units. Age, handgrip strength, CRP, suPAR, NGAL and smoking status had significant association with eGFR discrepancies between creatinine- and cystatin C-based equations.

Significant discrepancies in eGFR and CKD classification were observed when switching between eGFR equations in acutely hospitalized elderly patients. Switching from a creatinine-based equation to its corresponding cystatin C-based equation resulted in lower GFR estimates, and these differences were larger than in community-dwelling older populations. Switching between CKD-EPI_Cr , CG_Cr and the alternative equations would result in clinically relevant changes to medication prescribing. Discrepancies between equations were associated with high age, muscle weakness and inflammation.