title: Measured creatinine clearance from timed urine collections substantially overestimates glomerular filtration rate in patients with liver cirrhosis: a systematic review and individual patient meta-analysis.
abstract: BACKGROUND
  Accurate glomerular filtration rate (GFR) assessment in patients with liver cirrhosis is important for prognostication, chronic kidney disease staging, drug dosing and identifying combined liver-kidney transplantation candidates. The objective of this study was to review the accuracy of measured creatinine clearance (MCrCl) from timed urine collections for estimating true GFR.
  
  
  METHODS
  A systematic review and individual patient meta-analysis was performed. MEDLINE, old MEDLINE, Index Medicus and Cochrane library bibliographic databases and conference proceedings were searched up to June 2004. Reference lists of relevant studies were searched and experts were contacted. Comparative diagnostic studies describing stable adult patients with cirrhosis categorized according to the Child-Pugh classification were included if a gold standard GFR measurement was performed within 3 days of MCrCl. Individual patient data were abstracted from graphs of primary articles to allow a pooled analysis of agreement between renal measures.
  
  
  RESULTS
  Seven studies of 193 patients from 1974 to 2002 were summarized. MCrCl overestimated inulin clearance (CIn) by a mean of +13 ml/min/1.73 m2 and the limits of agreement (mean of the differences+/-2 SD) were +60 ml/min/1.73 m2 and -34 ml/min/1.73 m2. This overestimation was highest in patients with lower GFR. The mean clearance ratios [95% confidence interval (CI)] between MCrCl and CIn in the high (> or =60 ml/min/1.73 m2) and low (<60 ml/min/1.73 m2) GFR subgroups were 1.18 (1.12-1.23) and 1.49 (1.33-1.66), respectively (P<0.0001). Fourteen percent of patients with a MCrCl > or =60 ml/min/1.73 m2 had a CIn of <30 ml/min/1.73 m2.
  
  
  CONCLUSIONS
  For patients with liver cirrhosis, MCrCl from timed urine collections consistently overestimates the true GFR. For patients requiring complete clinical evaluation, GFR assessment by CIn is justified.
authors.affiliation: Department of Medicine, University of Western Ontario, London, Ontario N6A 4G5, Canada. nproulx@uwo.ca
authors.forename: Normand L
authors.initials: NL
authors.lastname: Proulx
authors.forename: Ayub
authors.initials: A
authors.lastname: Akbari
authors.forename: Amit X
authors.initials: AX
authors.lastname: Garg
authors.forename: Alaa
authors.initials: A
authors.lastname: Rostom
authors.forename: Jim
authors.initials: J
authors.lastname: Jaffey
authors.forename: Heather D
authors.initials: HD
authors.lastname: Clark
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D003404:Creatinine / Q000652:urine*; D005260:Female; D005919:Glomerular Filtration Rate; D006801:Humans; D007328:Insulin / Q000378:metabolism; D008103:Liver Cirrhosis / Q000652:urine*; D008297:Male; D008657:Metabolic Clearance Rate; D008875:Middle Aged
chemical_list: D007328:Insulin; D003404:Creatinine