Cystatin C and the Future of Kidney Function Assessment

In an interview with Pharmacy Times, Erin Barreto, PharmD, PhD, RPh, BCCCP, associate professor of medicine and pharmacy at Mayo Clinic in Rochester and a critical care pharmacist whose research focuses on optimizing renally active medications, discussed how emerging kidney biomarkers could change renal drug dosing and what hospital pharmacists should change about kidney function assessment today.

Barreto presented these insights during a presentation at the American Society of Nephrology’s 2026 Kidney Week, which took place October 21–25 in Denver, Colorado.

Barreto noted that creatinine has long been the primary marker of glomerular filtration rate (GFR), but new biomarkers of kidney health are entering practice. She described 2 categories: functional biomarkers, which quantify GFR for drug dosing, and structural or damage markers, which may help evaluate drug-associated harm, nephrotoxicity, and acute kidney injury. Cystatin C is the functional biomarker getting the most attention; although it has existed for decades, it is relatively new to medication decision-making, with new standardized equations, a growing presence in kidney guidelines, and expanding literature on medication management.

For hospital pharmacists today, Barreto said the biggest shift is moving from Cockcroft-Gault–based creatinine clearance to estimated GFR (eGFR) using an equation such as the Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equation, in line with recent efforts to standardize GFR assessment for medication dosing. She cautioned that the change is not trivial. It requires stakeholder engagement, clinician education, and extensive electronic health record integration so clinical decision support aligns with the new approach, and because eGFR is natively expressed in mL/min/1.73 m², it must be re-expressed in mL/min for drug dosing.

A harmonized, field-wide approach to cystatin C has yet to develop, she said.