title: Effect of preanalytical variables on myeloperoxidase levels.
abstract: BACKGROUND
  Myeloperoxidase (MPO) levels have prognostic value in cardiovascular events, but information about preanalytical variables is scarce. This study evaluated the effect of different sample types and storage conditions on MPO measurements.
  
  
  METHODS
  Plasma and serum samples [heparinized plasma (MPO-Hep), EDTA plasma (MPO-EDTA), and serum with (MPO-Gel) and without separator gel (MPO-Serum)] from 40 volunteers were assayed for MPO by ELISA (Bioxytech MPO-EIAkit). To evaluate MPO stability, samples were stored at 18-25 °C, at 2-8 °C and at -20 °C and -80 °C for predetermined periods.
  
  
  RESULTS
  MPO levels ranged from 16 to 69 ng/ml and were higher in patients with heart disease compared to healthy volunteers (35.0 vs. 24.9 ng/ml; P=0.03). There were no statistical differences between MPO-Hep, MPO-Gel and MPO-Serum (P>0.05), and MPO-Hep showed a good correlation with MPO-Gel and MPO-Serum (r=0.775 and r=0.792; P<0.001). No correlation between MPO-Hep and MPO-EDTA was found (r=0.21; P=0.20), and mean MPO-EDTA value was 1.8 times higher than MPO-Hep (51.4 vs. 28.7 ng/ml; P<0.001). Mean differences (ng/ml) between MPO-Hep and MPO-EDTA, MPO-Gel and MPO-Serum were 24.7 (19.5-30.0), 0.225 (-2.54-2.99), and 1.55 (-1.16-4.26), respectively.
  
  
  CONCLUSIONS
  EDTA had a significant effect on MPO results. MPO-Hep values correlate well with MPO-Gel and MPO-Serum. MPO levels seem to be stably frozen at -20 °C or -80 °C over 6 months depending on preanalytical handling.
authors.affiliation: Central Public Health Laboratory, Porto Alegre, Brazil; Cardiology Graduate Program, Federal University of Rio Grande do Sul, Brazil.
authors.forename: Andrea Elisabet
authors.initials: AE
authors.lastname: Wendland
authors.forename: Joíza Lins
authors.initials: JL
authors.lastname: Camargo
authors.forename: Carisi Anne
authors.initials: CA
authors.lastname: Polanczyk
mesh_terms: D004492:Edetic Acid / Q000494:pharmacology; D004797:Enzyme-Linked Immunosorbent Assay / Q000379:methods; D005782:Gels / Q000494:pharmacology; D006331:Heart Diseases / Q000201:enzymology; D006493:Heparin / Q000494:pharmacology; D006801:Humans; D009195:Peroxidase / Q000097:blood*; D055550:Protein Stability; D015203:Reproducibility of Results; D012107:Research Design / Q000592:standards; D044967:Serum; D013048:Specimen Handling / Q000379:methods / Q000592:standards*; D013696:Temperature
chemical_list: D005782:Gels; D006493:Heparin; D004492:Edetic Acid; D009195:Peroxidase