title: Performance of cystatin C- and creatinine-based estimated glomerular filtration rate equations depends on patient characteristics.
abstract: BACKGROUND
  The Kidney Disease Improving Global Outcomes (KDIGO) guideline recommends use of a cystatin C-based estimated glomerular filtration rate (eGFR) to confirm creatinine-based eGFR between 45 and 59 mL · min(-1) · (1.73 m(2))(-1). Prior studies have demonstrated that comorbidities such as solid-organ transplant strongly influence the relationship between measured GFR, creatinine, and cystatin C. Our objective was to evaluate the performance of cystatin C-based eGFR equations compared with creatinine-based eGFR and measured GFR across different clinical presentations.
  
  
  METHODS
  We compared the performance of the CKD-EPI 2009 creatinine-based estimated GFR equation (eGFRCr) and the newer CKD-EPI 2012 cystatin C-based equations (eGFRCys and eGFRCr-Cys) with measured GFR (iothalamate renal clearance) across defined patient populations. Patients (n = 1652) were categorized as transplant recipients (n = 568 kidney; n = 319 other organ), known chronic kidney disease (CKD) patients (n = 618), or potential kidney donors (n = 147).
  
  
  RESULTS
  eGFRCr-Cys showed the most consistent performance across different clinical populations. Among potential kidney donors without CKD [stage 2 or higher; eGFR >60 mL · min(-1) · (1.73 m(2))(-1)], eGFRCys and eGFRCr-Cys demonstrated significantly less bias than eGFRCr; however, all 3 equations substantially underestimated GFR when eGFR was <60 mL · min(-1) · (1.73 m(2))(-1). Among transplant recipients with CKD stage 3B or greater [eGFR <45 mL · min(-1) · (1.73 m(2))(-1)], eGFRCys was significantly more biased than eGFRCr. No clear differences in eGFR bias between equations were observed among known CKD patients regardless of eGFR range or in any patient group with a GFR between 45 and 59 mL · min(-1) · (1.73 m(2))(-1).
  
  
  CONCLUSIONS
  The performance of eGFR equations depends on patient characteristics that are readily apparent on presentation. Among the 3 CKD-EPI equations, eGFRCr-Cys performed most consistently across the studied patient populations.
authors.affiliation: Department of Laboratory Medicine and Pathology.
authors.forename: Jeffrey W
authors.initials: JW
authors.lastname: Meeusen
authors.affiliation: Department of Internal Medicine, Division of Nephrology and Hypertension, and Department of Health Sciences Research Division of Epidemiology, Mayo Clinic, Rochester, MN.
authors.forename: Andrew D
authors.initials: AD
authors.lastname: Rule
authors.affiliation: Department of Laboratory Medicine and Pathology.
authors.forename: Nikolay
authors.initials: N
authors.lastname: Voskoboev
authors.affiliation: Department of Laboratory Medicine and Pathology.
authors.forename: Nikola A
authors.initials: NA
authors.lastname: Baumann
authors.affiliation: Department of Laboratory Medicine and Pathology, Department of Internal Medicine, Division of Nephrology and Hypertension, and lieske.john@mayo.edu.
authors.forename: John C
authors.initials: JC
authors.lastname: Lieske
mesh_terms: D000328:Adult; D000368:Aged; D000465:Algorithms; D003404:Creatinine / Q000097:blood*; D055316:Cystatin C / Q000097:blood*; D005260:Female; D005919:Glomerular Filtration Rate; D006801:Humans; D007668:Kidney / Q000473:pathology; D016030:Kidney Transplantation; D008297:Male; D008875:Middle Aged; D051436:Renal Insufficiency, Chronic / Q000097:blood* / Q000175:diagnosis
chemical_list: D055316:Cystatin C; D003404:Creatinine