title: Macromolecular complexes of cystatin C with circulating liver plasma membrane fragments and determination of serum cystatin C using the particle enhanced nephelometric immunoassay (PENIA) in kidney and liver transplantation and biliary obstruction.
abstract: BACKGROUND
  In a patient with biliary obstruction, a macromolecular complex of cystatin C with liver plasma membrane fragments, which also contain several membrane-bound enzymes, which may be removed by butanol extraction, has recently been characterised. This could lead to an underestimation of the glomerular filtration rate (GFR) from serum cystatin C concentration.
  
  
  METHODS
  Using the particle enhanced nephelometric immunoassay (PENIA), serum cystatin C concentration was determined in 50 healthy controls, 43 patients with renal insufficiency, 68 kidney and 88 liver transplant recipients, and 60 patients with biliary obstruction. Residual cystatin C concentrations and gamma-glutamyltransferase (GGT) activities after butanol extraction were also determined.
  
  
  RESULTS
  In the controls and patients with renal insufficiency the residual concentrations of cystatin C after butanol extraction were always > or = 80%. However, in 2 renal and 7 liver transplant recipients and in 11 patients with biliary obstruction this biochemical variable was < 80%. A significant correlation between the residual cystatin C concentrations and residual GGT activities was obtained (r = 0.386, p < 0.001). In the relationship between estimated GFR from serum cystatin C and creatinine concentrations in the liver transplant recipients and patients with biliary obstruction, the 18 cases with residual cystatin C concentrations < 80% were included in the distribution of the total population data with no particular tendency.
  
  
  CONCLUSIONS
  These results suggest that in the cases with residual cystatin C concentrations < 80% after butanol extraction, presumably due to the presence of circulating macromolecular cystatin C, the serum levels of cystatin C obtained using the PENIA assay do not lead to a systematic GFR underestimation.
authors.affiliation: Unidad Monitorización Fármacos, Laboratorio Central, Hospital Clínico Universitario, Instituto Investigacion Sanitaria (IDIS), Santiago de Compostela, Spain.
authors.forename: Lorena
authors.initials: L
authors.lastname: Bouzas
authors.forename: J Carlos
authors.initials: JC
authors.lastname: Tutor
mesh_terms: D002462:Cell Membrane / Q000473:pathology; D002779:Cholestasis / Q000097:blood; D055316:Cystatin C / Q000097:blood*; D006801:Humans; D007118:Immunoassay; D016030:Kidney Transplantation / Q000473:pathology; D008099:Liver / Q000473:pathology; D016031:Liver Transplantation / Q000473:pathology; D009391:Nephelometry and Turbidimetry / Q000379:methods; D051437:Renal Insufficiency / Q000473:pathology
chemical_list: D055316:Cystatin C