title: GFR Estimation Using β-Trace Protein and β2-Microglobulin in CKD.
abstract: BACKGROUND
  β-Trace protein (BTP) and β2-microglobulin (B2M) are novel glomerular filtration markers that have stronger associations with adverse outcomes than creatinine. Comparisons of BTP and B2M to creatinine and cystatin C are limited by the absence of rigorously developed glomerular filtration rate (GFR) estimating equations for the novel markers.
  
  
  METHODS
  Study of diagnostic test accuracy.
  
  
  METHODS
  Pooled database of 3 populations with chronic kidney disease (CKD) with mean measured GFR of 48 mL/min/1.73 m2 (N=3,551; MDRD [Modification of Diet in Renal Disease] Study, AASK [African American Study of Kidney Disease and Hypertension], and CRIC [Chronic Renal Insufficiency Cohort] Study).
  
  
  METHODS
  GFR estimated using creatinine, cystatin C, BTP, or B2M level.
  
  
  METHODS
  GFR measured as the urinary clearance of iothalamate.
  
  
  RESULTS
  For BTP and B2M, coefficients for age, sex, and race were smaller than for creatinine and were similar or smaller than for cystatin C. For B2M, coefficients for sex, age, and race were smaller than for creatinine and were similar (age and race) or smaller (sex) than for cystatin C. The final equations with BTP (BTP, age, and sex) or B2M (B2M alone) were less accurate than either the CKD-EPI (CKD Epidemiology Collaboration) creatinine or cystatin C equations. The combined BTP-B2M equation (BTP and B2M alone) had similar accuracy to the CKD-EPI creatinine or cystatin C equation. The average of the BTP-B2M equation and the CKD-EPI creatinine-cystatin C equation was not more accurate than the CKD-EPI creatinine-cystatin C equation.
  
  
  CONCLUSIONS
  No external validation population, study population was restricted to CKD, few participants older than 65 years, or nonblack nonwhite race.
  
  
  CONCLUSIONS
  BTP and B2M are less influenced by age, sex, and race than creatinine and less influenced by race than cystatin C, but provide less accurate GFR estimates than the CKD-EPI creatinine and cystatin C equations. The CKD-EPI BTP and B2M equation provides a methodological advance for their study as filtration markers and in their associations with risk and adverse outcomes, but further study is required before clinical use.
authors.affiliation: Tufts Medical Center, Boston, MA. Electronic address: linker@tuftsmedicalcenter.org.
authors.forename: Lesley A
authors.initials: LA
authors.lastname: Inker
authors.affiliation: Tufts Medical Center, Boston, MA; Research Design Center/Biostatistics Research Center, Tufts CTSI and Institute for Clinical Research and Health Policy Studies, Boston, MA.
authors.forename: Hocine
authors.initials: H
authors.lastname: Tighiouart
authors.affiliation: Johns Hopkins University School of Medicine, Baltimore, MD.
authors.forename: Josef
authors.initials: J
authors.lastname: Coresh
authors.affiliation: Tufts Medical Center, Boston, MA.
authors.forename: Meredith C
authors.initials: MC
authors.lastname: Foster
authors.affiliation: Perelman School of Medicine at the University of Pennsylvania. Philadelphia, PA.
authors.forename: Amanda H
authors.initials: AH
authors.lastname: Anderson
authors.affiliation: Cleveland Clinic, Cleveland, OH.
authors.forename: Gerald J
authors.initials: GJ
authors.lastname: Beck
authors.affiliation: University of Miami Miller School of Medicine, Miami, FL.
authors.forename: Gabriel
authors.initials: G
authors.lastname: Contreras
authors.affiliation: University of Utah, Salt Lake City, UT.
authors.forename: Tom
authors.initials: T
authors.lastname: Greene
authors.affiliation: University of Minnesota, Minneapolis, MN.
authors.forename: Amy B
authors.initials: AB
authors.lastname: Karger
authors.affiliation: National Institute of Diabetes and Digestive and Kidney Diseases, Bethesda, MD.
authors.forename: John W
authors.initials: JW
authors.lastname: Kusek
authors.affiliation: University of Illinois at Chicago, Chicago, IL.
authors.forename: James
authors.initials: J
authors.lastname: Lash
authors.affiliation: Vanderbilt Medical Center, Nashville, TN.
authors.forename: Julia
authors.initials: J
authors.lastname: Lewis
authors.affiliation: Case Western Reserve University, MetroHealth Medical Center, Cleveland, OH.
authors.forename: Jeffrey R
authors.initials: JR
authors.lastname: Schelling
authors.affiliation: Cleveland Clinic, Cleveland, OH.
authors.forename: Sankar D
authors.initials: SD
authors.lastname: Navaneethan
authors.affiliation: Wayne State University, Detroit, MI.
authors.forename: James
authors.initials: J
authors.lastname: Sondheimer
authors.affiliation: Johns Hopkins University School of Medicine, Baltimore, MD.
authors.forename: Tariq
authors.initials: T
authors.lastname: Shafi
authors.affiliation: Tufts Medical Center, Boston, MA.
authors.forename: Andrew S
authors.initials: AS
authors.lastname: Levey
mesh_terms: D000328:Adult; D000368:Aged; D015415:Biomarkers / Q000097:blood; D015331:Cohort Studies; D003404:Creatinine / Q000097:blood; D055316:Cystatin C / Q000097:blood; D005260:Female; D005919:Glomerular Filtration Rate; D006801:Humans; D019746:Intramolecular Oxidoreductases / Q000097:blood*; D054834:Lipocalins / Q000097:blood*; D008297:Male; D008875:Middle Aged; D051436:Renal Insufficiency, Chronic / Q000097:blood* / Q000503:physiopathology*; D015203:Reproducibility of Results; D001613:beta 2-Microglobulin / Q000097:blood
chemical_list: D015415:Biomarkers; D055316:Cystatin C; D054834:Lipocalins; D001613:beta 2-Microglobulin; D003404:Creatinine; D019746:Intramolecular Oxidoreductases; C022466:prostaglandin R2 D-isomerase
keywords: Beta-trace protein (BTP); beta-2-microglobulin (B2M); chronic kidney disease (CKD); diagnostic accuracy; estimated glomerular filtration rate (eGFR); estimating equation; filtration marker; kidney function; measured GFR