title: AlphaLISA versus ELISA-based detection of interleukin 18 in healthy subjects and patients with end-stage renal disease.
abstract: BACKGROUND
  Interleukin 18 (IL-18) is an important pro-inflammatory cytokine investigated in end-stage renal disease (ESRD) and several autoimmune and inflammatory diseases. The quantitative colorimetric sandwich ELISA test kit from MBL is the most frequently used ELISA kit for IL-18 detection. Recently, a new bead-based proximity assay named AlphaLISA was developed. The aim of this study was to compare the performance of these two kits and to evaluate aspects of sample handling on IL-18 measurements.
  
  
  METHODS
  Measurements of IL-18 were performed on plasma samples from 11 ESRD-patients in regular haemodialysis treatment and 10 healthy volunteers.
  
  
  RESULTS
  We found a significant difference between assays corresponding to a factor of 6.4 (6.0; 6.7), p < 0.0001. Agreement was excellent with intra-class correlation coefficient 0.95. MBL had lower inter-assay variation, batch-to-batch variation and day-to-day variation. Spiking with recombinant IL-18 resulted in a mean recovery of 91 ± 7 (MBL) vs. 135 ± 17% (AlphaLISA), p < 0.0001. Both kits performed equally well when linearity was investigated. IL-18 was stable over a period of 424 days when plasma samples were stored at - 80°C. When blood samples were stored at room temperature mean IL-18 concentration changed significantly between 0, 1, 6, and 24 hours after sampling (p = 0.0213). No significant change was found with storage at 5°C. Severe haemolysis affected IL-18 measurements, whereas repeated freezing and thawing showed no effect. Mean IL-18 concentration was significantly higher in ESRD-patients compared to healthy subjects regardless of assay.
  
  
  CONCLUSIONS
  Assay performance was best with the MBL-kit, although AlphaLISA was less time consuming when measuring plasma IL-18.
authors.affiliation: Department of Renal Medicine, Aarhus University Hospital, Skejby, Denmark. cdp@ana.au.dk
authors.forename: Christian D
authors.initials: CD
authors.lastname: Peters
authors.forename: Bente
authors.initials: B
authors.lastname: Jespersen
authors.forename: Rikke
authors.initials: R
authors.lastname: Nørregaard
mesh_terms: D000906:Antibodies; D002138:Calibration; D004797:Enzyme-Linked Immunosorbent Assay / Q000379:methods*; D005615:Freezing; D006262:Health; D006461:Hemolysis; D006801:Humans; D020382:Interleukin-18 / Q000097:blood*; D007676:Kidney Failure, Chronic / Q000097:blood*; D057230:Limit of Detection; D011309:Preservation, Biological; D055550:Protein Stability; D011933:Reagent Kits, Diagnostic; D012015:Reference Standards; D013696:Temperature; D013997:Time Factors
chemical_list: D000906:Antibodies; D020382:Interleukin-18; D011933:Reagent Kits, Diagnostic