title: Estimated glomerular filtration rate (eGFRCystC) from serum cystatin C shows strong agreement with iohexol clearance in patients with low GFR.
abstract: OBJECTIVE
  Estimation of glomerular filtration rate (eGFR) is essential in the diagnosis and monitoring of patients with kidney disease and for correct dosage of drugs eliminated from the circulation by the kidneys. Cystatin C has been shown in several studies to be superior to creatinine in estimating eGFR. However, there are few studies on the performance of cystatin C estimated eGFR (eGFRCystC) in patients with advanced kidney disease and low GFR.
  
  
  METHODS
  We measured serum cystatin C, together with serum creatinine, during iohexol clearance in patients with iohexol clearance below 30 mL/min/1.73 m2. The cystatin C values were used to calculate eGFRCystC using the formula eGFR (mL/min/1.73 m2) = 79.901*(cystatin C value in mg/L)-1.4389.
  
  
  RESULTS
  There was good correlation between eGFRCystC and iohexol clearance (r = 0.88) in patients with iohexol clearance <30 mL/min/1.73 m2 and none of the patients had a difference between eGFRCystC and iohexol clearance exceeding 50 %. The Modification of Diet in Renal Disease (MDRD) equation and corrected MDRD eGFR showed a positive bias and weaker correlations with iohexol eGFR (MDRD = 5.32+1.22*iohexol clearance; corrected MDRD = 4.76+1.10*iohexol clearance; r = 0.59). For MDRD eGFR, 42 of 94 (44.7%) samples showed more than 50% difference to iohexol clearance.
  
  
  CONCLUSIONS
  eGFRCystC is an efficient, practical and cost-effective alternative to iohexol clearance in patients with reduced GFR.
authors.affiliation: Department of Clinical Chemistry, Karlstad, Sweden.
authors.forename: A-S
authors.initials: AS
authors.lastname: Jonsson
authors.forename: M
authors.initials: M
authors.lastname: Flodin
authors.forename: L-O
authors.initials: LO
authors.lastname: Hansson
authors.forename: A
authors.initials: A
authors.lastname: Larsson
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D003404:Creatinine / Q000097:blood; D055316:Cystatin C; D015891:Cystatins / Q000097:blood*; D005260:Female; D005919:Glomerular Filtration Rate / Q000502:physiology*; D006801:Humans; D007472:Iohexol / Q000493:pharmacokinetics*; D008297:Male; D008657:Metabolic Clearance Rate; D008875:Middle Aged
chemical_list: C525030:CST3 protein, human; D055316:Cystatin C; D015891:Cystatins; D007472:Iohexol; D003404:Creatinine