title: Cystatin-C and beta trace protein as markers of renal function in pregnancy.
abstract: OBJECTIVE
  To assess the validity of Cystatin-C (Cys-C) and beta trace protein (BTP) as clinical markers of glomerular filtration rate (GFR) in pregnant women.
  
  
  METHODS
  Prospective cross sectional study.
  
  
  METHODS
  Obstetric unit of a tertiary care hospital.
  
  
  METHODS
  One hundred and thirty-seven normal pregnant women and 13 women postpartum.
  
  
  METHODS
  Twenty-four hour creatinine clearance (CrCl), serum creatinine, Cys-C and BTP concentrations were measured on normal pregnant women in the first trimester (n= 5), second trimester (n= 68) and third trimester (n= 64) and in 13 women postpartum. Data are given as median (2.5th centile, 97.5th centile).
  
  
  METHODS
  Serum concentrations of Cys-C and BTP compared with creatinine clearance and serum creatinine.
  
  
  RESULTS
  The median serum creatinine throughout gestation was 53 micromol/L (39, 71), and median CrCl was 143 mL/minute (91 to 216). Postpartum, creatinine rose to 74 micromol/L (58, 86) and CrCl decreased to 104 mL/minute (71, 159). For Cys-C, the median concentration was 0.70 mg/L (0.46, 1.32), and 0.54 mg/L (0.36, 0.96) for BTP. Comparing the second and third trimesters, there was no significant difference between CrCl (median 145 vs 141 mL/minute) and BTP concentrations (median 0.51 vs 0.55 mg/L), while median Cys-C was significantly higher in the third trimester (0.61 vs 0.88 mg/L; P < 0.001). Unlike creatinine and BTP, Cys-C levels decreased to 0.72 mg/L (0.57, 0.95) postpartum. The only significant relationship of either of these markers to the standard used for GFR was between Cys-C and CrCl in the third trimester, and the correlation was weak (r= 0.27 for 1/Cys-C vs CrCl).
  
  
  CONCLUSIONS
  These data demonstrate that despite claims to the contrary, Cys-C is a poor marker of GFR during pregnancy. Similarly, BTP shows little promise.
authors.affiliation: Kidney Research Centre, Ottawa, Ontario, Canada.
authors.forename: Ayub
authors.initials: A
authors.lastname: Akbari
authors.forename: Nathalie
authors.initials: N
authors.lastname: Lepage
authors.forename: Erin
authors.initials: E
authors.lastname: Keely
authors.forename: Heather D
authors.initials: HD
authors.lastname: Clark
authors.forename: James
authors.initials: J
authors.lastname: Jaffey
authors.forename: Martin
authors.initials: M
authors.lastname: MacKinnon
authors.forename: Guido
authors.initials: G
authors.lastname: Filler
mesh_terms: D015415:Biomarkers / Q000097:blood; D003430:Cross-Sectional Studies; D055316:Cystatin C; D015891:Cystatins / Q000097:blood*; D005260:Female; D005919:Glomerular Filtration Rate / Q000502:physiology*; D006801:Humans; D019746:Intramolecular Oxidoreductases / Q000097:blood*; D007674:Kidney Diseases / Q000175:diagnosis; D054834:Lipocalins; D011247:Pregnancy / Q000502:physiology*; D011248:Pregnancy Complications / Q000175:diagnosis; D011296:Prenatal Diagnosis / Q000379:methods*; D011446:Prospective Studies
chemical_list: D015415:Biomarkers; C525030:CST3 protein, human; D055316:Cystatin C; D015891:Cystatins; D054834:Lipocalins; D019746:Intramolecular Oxidoreductases; C022466:prostaglandin R2 D-isomerase