title: C-reactive protein levels in patients on maintenance hemodialysis: reliability and reflection on the utility of single measurements.
abstract: BACKGROUND
  Single C-reactive protein (CRP) values have been associated with death and cardiovascular disease in dialysis patients. We prospectively obtained multiple CRP values in stable patients, hypothesizing that values would remain stable in the absence of disease and that a single CRP value would be a reliable marker of risk.
  
  
  METHODS
  Four CRP values per week for three consecutive weeks were obtained in 10 clinically stable patients receiving conventional HD. Using prespecified cutoffs of 2.2 and 4.4 mg/l, the frequency of risk misclassification relative to the lowest CRP value obtained was determined. Within and between patient variability was also calculated.
  
  
  RESULTS
  The median age was 54 years, and the average duration of dialysis was 41 months. Nine out of ten patients had at least one abnormal CRP value (>2.2 mg/l), six had all values elevated, and seven had an abnormal median CRP. The overall coefficient of reliability was 0.63 (95% CI 0.42-0.87). The misclassification rate varied with cutoff, and ranged from 0-83% and 0-58% using upper limit of normal (ULN) and twice ULN, respectively. The within patient variability was 0.37 for the entire cohort, and 0.33 when three patients with intercurrent acute inflammation were excluded.
  
  
  CONCLUSIONS
  CRP exhibits short term variability in HD patients, resulting in a risk of misclassification depending on sampling time and chosen cutoff point. Single CRP values must be interpreted with caution, and multiple measurements, or use of other biomarkers, should be considered.
authors.affiliation: Kidney Foundation of Canada Research Fellow, Division of Nephrology, University of British Columbia, British Columbia, Canada.
authors.forename: Caroline E
authors.initials: CE
authors.lastname: Stigant
authors.forename: Ognjenka
authors.initials: O
authors.lastname: Djurdjev
authors.forename: Adeera
authors.initials: A
authors.lastname: Levin
mesh_terms: D000368:Aged; D015415:Biomarkers / Q000097:blood; D002097:C-Reactive Protein / Q000032:analysis*; D005260:Female; D006801:Humans; D007249:Inflammation / Q000175:diagnosis; D007676:Kidney Failure, Chronic / Q000097:blood* / Q000628:therapy; D008297:Male; D008875:Middle Aged; D011379:Prognosis; D011446:Prospective Studies; D006435:Renal Dialysis; D015203:Reproducibility of Results; D018570:Risk Assessment; D013997:Time Factors
chemical_list: D015415:Biomarkers; D002097:C-Reactive Protein