title: Long-term stability of endogenous B-type natriuretic peptide during storage at -20 degrees C for later measurement with Biosite Triage assay.
abstract: OBJECTIVE
  To evaluate the long-term stability of B-type natriuretic peptide (BNP) in frozen samples at -20 degrees C.
  
  
  METHODS
  During a health and nutrition survey of a representative sample of the adult population of Porto, Portugal, blood samples were collected in EDTA tubes. Aliquots of plasma were frozen at -20 degrees C until measurement. Subjects with cardiac structural or functional abnormalities or renal dysfunction were excluded. BNP was assessed using a commercial immunofluorescence assay (Triage BNP Test) as a continuous variable (n=340) and in four subgroups selected according to different storage periods: < or =1 month (n=35), 6-12 months (n=80), 20-24 months (n=18) and > or =36 months (n=21).
  
  
  RESULTS
  Age- and sex-adjusted BNP values, analyzed as a continuous variable, decreased significantly over time of storage. When we stratified in four intervals of storage time, the median BNP value (25th-75th percentile, p value) was: 22.6 pg/mL (8.9-76.2, reference group) for < or =1 month, 19.8 pg/mL (9.5-48.4, p=0.055) for 6-12 months, 15.3 pg/mL (7.5-35.0, p=0.037) for 20-24 months, and 2.5 pg/mL (2.5-10.5, p<0.001) for > or =36 months.
  
  
  CONCLUSIONS
  BNP is stable at -20 degrees C for 1 year, without protease inhibitors.
authors: Department of Hygiene and Epidemiology, University of Porto Medical School, Alameda Prof Hernâni Monteiro, 4200-319 Porto, Portugal. martasfp@med.up.pt
authors: Marta
authors: M
authors: Pereira
authors: Ana
authors: A
authors: Azevedo
authors: Milton
authors: M
authors: Severo
authors: Henrique
authors: H
authors: Barros
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D015925:Cryopreservation; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D020097:Natriuretic Peptide, Brain / Q000032:analysis / Q000737:chemistry* / Q000378:metabolism; D011489:Protein Denaturation; D011933:Reagent Kits, Diagnostic; D012107:Research Design; D013997:Time Factors
chemical_list: D011933:Reagent Kits, Diagnostic; D020097:Natriuretic Peptide, Brain