title: A comparison of plasma cystatin C and plasma creatinine for the screening of renal function in lithium-treated patients.
abstract: BACKGROUND
  Renal insufficiency is a serious complication of lithium treatment. Therefore, regular monitoring of plasma (P) creatinine is always part of lithium treatment safety routines. Recently P-cystatin C-estimated glomerular filtration rate (cystatin C-eGFR) had been launched as a preferable alternative to P-creatinine.
  
  
  OBJECTIVE
  To find out which of the two alternatives to prefer in the safety routines for lithium-treated patients.
  
  
  METHODS
  All 201 patients on lithium treatment at the Department of Psychiatry in Lund, Sweden.
  
  
  METHODS
  During 14 months P-cystatin C was included in the safety routines besides routine P-creatinine every 4 months. At the end of the study period, 182 patients were eligible for analysis. With iohexol clearance as reference for GFR (performed in 111/182 patients) we calculated positive and negative predictive values (PPV, NPV) for P-creatinine and for creatinine-eGFR and cystatin C-eGFR, obtained by prediction equations. We also calculated the agreement between the measures of GFR (including repeatability).
  
  
  RESULTS
  PPV for cystatin C-eGFR (65%) was better than for creatinine-eGFR (48%). Combining the two resulted in a PPV of 56% and marginally increased NPV to 95%. The average of cystatin C-eGFR and creatinine-eGFR yielded PPV 67% and NPV 92%. The agreement between creatinine-eGFR and GFR was better than the agreement between cystatin C-eGFR and GFR, but both were clinically unacceptable. The repeatability of P-creatinine was acceptable for psychiatric purposes. The repeatability of cystatin C-eGFR was inferior to that of P-creatinine.
  
  
  CONCLUSIONS
  Our results do not justify replacing P-creatinine by cystatin C-eGFR in the lithium treatment safety routines.
authors.affiliation: Department of Psychiatry, Malmö University Hospital, Malmö, Sweden.
authors.forename: C L
authors.initials: CL
authors.lastname: Olsson
authors.forename: B
authors.initials: B
authors.lastname: Rippe
authors.forename: H
authors.initials: H
authors.lastname: Bendz
mesh_terms: D015415:Biomarkers / Q000097:blood; D003287:Contrast Media / Q000493:pharmacokinetics; D003404:Creatinine / Q000097:blood*; D055316:Cystatin C / Q000097:blood*; D005260:Female; D005919:Glomerular Filtration Rate; D006801:Humans; D007472:Iohexol / Q000493:pharmacokinetics; D007677:Kidney Function Tests / Q000379:methods*; D008094:Lithium / Q000008:administration & dosage* / Q000009:adverse effects*; D008297:Male; D008875:Middle Aged; D011237:Predictive Value of Tests; D012044:Regression Analysis; D015203:Reproducibility of Results
chemical_list: D015415:Biomarkers; D003287:Contrast Media; D055316:Cystatin C; D007472:Iohexol; D008094:Lithium; D003404:Creatinine