title: Parathormone stability in hemodialyzed patients and healthy subjects: comparison on non-centrifuged EDTA and serum samples with second- and third-generation assays.
abstract: BACKGROUND
  Parathyroid hormone (PTH) stability is important. Many studies have shown divergent results between EDTA and serum, which are mainly linked to differences in protocols or cut-offs used to determine whether or not PTH remained stable. No studies have yet compared PTH stability as measured by second- and third-generation assays on the same samples in hemodialyzed patients and healthy subjects.
  
  
  METHODS
  Five pairs of samples (EDTA and gel tubes) were obtained in 10 hemodialyzed patients before a dialysis session and in 10 healthy subjects. One pair was centrifuged and run directly to define the "T0". Two pairs were kept at +4°C and two pairs were kept at +25°C. They were centrifuged after 4 and 18 h. Supernatant was kept at -80°C for 1 week. All samples were measured in a single batch, on Roche Cobas and DiaSorin XL second- and third-generation PTH assays. We used three different approaches to evaluate PTH stability: Wilcoxon test, an Acceptable Change Limit (ACL) according to ISO Guide 5725-6 and a Total Change Limit (TCL) derived from the sum of biological and technical variability according to WHO.
  
  
  RESULTS
  PTH decreased in all samples. Stability of PTH was mainly dependent on the way it was evaluated. Percentages of decrease were systematically lower in EDTA vs. serum. Wilcoxon and ACL showed that PTH was no more stable after 4 h at +4°C in EDTA or serum gel tubes. None of the subjects presented a PTH decrease higher than the TCL with EDTA plasma. In serum gel tubes, PTH was unstable only when kept at 25°C for 18 h.
  
  
  CONCLUSIONS
  PTH seems more stable in EDTA than in serum gel tubes but only when samples have to stay unprocessed for a long period (18 h) at room temperature (25°C), which can happen when samples are delivered from external care centers. For all the other conditions, using serum gel tubes is recommended since calcium measurement, which is necessary for a good PTH results interpretation, can be achieved on the same tube.
authors.affiliation: .
authors.forename: Marie-Louise
authors.identifier: http://orcid.org/0000-0002-0270-1711
authors.initials: ML
authors.lastname: Schleck
authors.affiliation: .
authors.forename: Jean-Claude
authors.initials: JC
authors.lastname: Souberbielle
authors.affiliation: .
authors.forename: Pierre
authors.initials: P
authors.lastname: Delanaye
authors.affiliation: .
authors.forename: Mario
authors.identifier: http://orcid.org/0000-0002-0270-1711
authors.initials: M
authors.lastname: Plebani
authors.affiliation: .
authors.forename: Etienne
authors.initials: E
authors.lastname: Cavalier
mesh_terms: D000328:Adult; D016477:Artifacts; D001774:Blood Chemical Analysis / Q000379:methods*; D001800:Blood Specimen Collection; D002498:Centrifugation; D004492:Edetic Acid / Q000737:chemistry*; D005260:Female; D064368:Healthy Volunteers; D006801:Humans; D008297:Male; D008875:Middle Aged; D010281:Parathyroid Hormone / Q000097:blood* / Q000302:isolation & purification; D006435:Renal Dialysis; D015203:Reproducibility of Results; D013696:Temperature; D055815:Young Adult
chemical_list: D010281:Parathyroid Hormone; D004492:Edetic Acid
keywords: biological variation; parathyroid hormone; stability