title: Long-term stability of endogenous B-type natriuretic peptide after storage at -20 degrees C or -80 degrees C.
abstract: BACKGROUND
  B-type natriuretic peptide (BNP) is a biomarker used in the investigation of heart failure and other cardiovascular diseases. Our aim was to analyze the degradation of BNP in plasma samples kept at -20 degrees C or at -80 degrees C after 3 months or 1 year of storage.
  
  
  METHODS
  Using a Biosite assay-Triage BNP test, we evaluated 20 subjects with plasma BNP concentrations ranging from normal to high. Plasma aliquots were separated in five eppendorfs, one for immediate measurement after centrifugation, two for storage at -20 degrees C and two at -80 degrees C. We measured BNP after 3 months and 1 year. The significance level was set at p<0.05 (one-tailed test).
  
  
  RESULTS
  There was a significant decrease of 1% per month in BNP concentration. However, there was a significant interaction between time and group (high vs. low BNP). Low BNP values did not change over time, while high BNP decreased by 2% per month. The decrease over time did not depend on the storage temperature.
  
  
  CONCLUSIONS
  The storage of the samples at -20 degrees C or at -80 degrees C did not prevent BNP degradation, especially for high BNP values. For low BNP values, we did not observe a significant decay at either 3 months or 1 year. These results are valid for the Biosite assay-Triage BNP test.
authors.affiliation: Department of Hygiene and Epidemiology, University of Porto Medical School, Cardiovascular R&D Unit, Porto, Portugal. martasfp@med.up.pt
authors.forename: Marta
authors.initials: M
authors.lastname: Pereira
authors.forename: Ana
authors.initials: A
authors.lastname: Azevedo
authors.forename: Milton
authors.initials: M
authors.lastname: Severo
authors.forename: Henrique
authors.initials: H
authors.lastname: Barros
mesh_terms: D000368:Aged; D003080:Cold Temperature; D005260:Female; D005615:Freezing; D006801:Humans; D008297:Male; D008875:Middle Aged; D020097:Natriuretic Peptide, Brain / Q000097:blood / Q000378:metabolism*; D013048:Specimen Handling / Q000379:methods*; D013997:Time Factors
chemical_list: D020097:Natriuretic Peptide, Brain