title: Estimation of the stability of parathyroid hormone when stored at -80 degrees C for a long period.
abstract: OBJECTIVE
  Stability of parathyroid hormone (PTH) at -80 degrees C for long storage periods has never been studied. This can be of importance for the conclusions of studies where blood banks have been constituted. The study's aim was to evaluate stability of PTH when stored as serum or plasma EDTA samples at -80 degrees C.
  
  
  METHODS
  Samples were collected from 16 chronic hemodialysis patients using EDTA and gel-separator tubes. Plasma and serum were aliquoted; one aliquot was assayed with Elecsys and Liaison methods to determine the "baseline" values and another aliquot after 1, 3, 6, and 12 mo. The factors "method," "tubes," "subjects," and "time" were included in a mixed linear model to evaluate their effects on measured PTH values. The prediction interval methodology was used to assess where a future result could be obtained with a defined probability.
  
  
  RESULTS
  With the Liaison method, the maximum storage times with either dry or EDTA tubes were estimated to be 9 and 2 mo, respectively. With the Elecsys method, samples could be stored at least 2 yr with acceptable level of degradation.
  
  
  CONCLUSIONS
  PTH stability at -80 degrees C is not infinite. Maximum storage time and acceptance limits (30%) were defined, showing that with one method, samples should be stored for not more than 2 mo, whereas the other could be stored for up to 2 yr. With any PTH assay, the maximum storage time should be evaluated to ascertain that samples will keep their initial reactive profile after prolonged storage periods.
authors.affiliation: Department of Clinical Chemistry, University of Liège, Domaine du Sart-Tilman, Liège, Belgium. Etienne.cavalier@chu.ulg.ac.be
authors.forename: Etienne
authors.initials: E
authors.lastname: Cavalier
authors.forename: Pierre
authors.initials: P
authors.lastname: Delanaye
authors.forename: Philippe
authors.initials: P
authors.lastname: Hubert
authors.forename: Jean-Marie
authors.initials: JM
authors.lastname: Krzesinski
authors.forename: Jean-Paul
authors.initials: JP
authors.lastname: Chapelle
authors.forename: Eric
authors.initials: E
authors.lastname: Rozet
mesh_terms: D000925:Anticoagulants; D001771:Blood Banks / Q000592:standards*; D002624:Chemistry, Clinical / Q000592:standards*; D003080:Cold Temperature; D015925:Cryopreservation / Q000592:standards*; D004492:Edetic Acid; D006801:Humans; D007676:Kidney Failure, Chronic / Q000097:blood / Q000628:therapy; D008954:Models, Biological; D010281:Parathyroid Hormone / Q000032:analysis* / Q000097:blood; D006435:Renal Dialysis; D015203:Reproducibility of Results; D013048:Specimen Handling
chemical_list: D000925:Anticoagulants; D010281:Parathyroid Hormone; D004492:Edetic Acid