DIAGNOSTICS AND TECHNIQUES: Edited by Maarten W. TaalCystatin C is ready for clinical useEbert, Nataliea; Shlipak, Michael G.bAuthor Information aInstitute of Public Health, Charité – Universitätsmedizin Berlin, Berlin, Germany bKidney Health Research Collaborative and Division of General Internal Medicine, San Francisco Veterans Affairs Medical Center, University of California San Francisco, San Francisco, CA, USA Correspondence to Natalie Ebert, MD, MPH, Institute of Public Health, Charité – Universitätsmedizin Berlin, Luisenstraße 57, 10117 Berlin, Germany. Tel: +49 30 450 653209; e-mail: firstname.lastname@example.org Current Opinion in Nephrology and Hypertension: November 2020 - Volume 29 - Issue 6 - p 591-598 doi: 10.1097/MNH.0000000000000638 Buy Metrics Abstract Purpose of review The goal of this update is to raise awareness of clinical scenarios where cystatin C has clear and immediate benefits as an alternative glomerular filtration rate (GFR) biomarker to supplement creatinine. An additional goal is to focus the estimated GFR (eGFR) controversy onto medication prescribing for agents with narrow therapeutic windows where better GFR estimation will lead to improved medical care. Recent findings Equations that include cystatin C predict GFR more accurately than serum creatinine in children, adults, and older adults with larger effects among persons who are acutely ill. Numerous studies have evaluated medication dosing based on either GFR estimate; vancomycin was the most frequently studied drug and its target level and elimination were better predicted by cystatin C. Overall, approaches to medication dosing and monitoring that include cystatin C concentrations have been shown to result in a better achievement of drug trough levels. Furthermore, cystatin C offers the opportunity to avoid the race coefficient that is required for any current creatinine-based eGFR equation, which has been appropriately criticized for introducing unnecessary imprecision, assumptions and values on GFR estimation. Summary Hospital laboratories must make cystatin C available for clinical care to improve the safety and efficacy of medications that have narrow therapeutic windows. Copyright © 2020 Wolters Kluwer Health, Inc. All rights reserved.