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Case Reports in Nephrology
Volume 2016 (2016), Article ID 9349280, 4 pages
Case Report

Cystatin C Falsely Underestimated GFR in a Critically Ill Patient with a New Diagnosis of AIDS

1Hospital Pharmacy Services, Mayo Clinic, 200 First Street SW, Rochester, MN 55905, USA
2Division of Pulmonary and Critical Care Medicine, Mayo Clinic, 200 First Street SW, Rochester, MN 55905, USA
3Division of Nephrology and Hypertension, Mayo Clinic, 200 First Street SW, Rochester, MN 55905, USA

Received 11 March 2016; Accepted 26 April 2016

Academic Editor: Anja Haase-Fielitz

Copyright © 2016 Caitlin S. Brown et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


Cystatin C has been suggested to be a more accurate glomerular filtration rate (GFR) surrogate than creatinine in patients with acquired immunodeficiency syndrome (AIDS) because it is unaffected by skeletal muscle mass and dietary influences. However, little is known about the utility of this marker for monitoring medications in the critically ill. We describe the case of a 64-year-old female with opportunistic infections associated with a new diagnosis of AIDS. During her course, she experienced neurologic, cardiac, and respiratory failure; yet her renal function remained preserved as indicated by an eGFR ≥ 120 mL/min and a urine output > 1 mL/kg/hr without diuresis. The patient was treated with nephrotoxic agents; therefore cystatin C was assessed to determine if cachexia was resulting in a falsely low serum creatinine. Cystatin C measured 1.50 mg/L which corresponded to an eGFR of 36 mL/min. Given the >60 mL/min discrepancy, serial 8-hour urine samples were collected and a GFR > 120 mL/min was confirmed. It is unclear why cystatin C was falsely elevated, but we hypothesize that it relates to the proinflammatory state with AIDS, opportunistic infections, and corticosteroids. More research is needed before routine use of cystatin C in this setting can be recommended.