title: Thrombin-mediated degradation of parathyroid hormone in serum tubes.
abstract: BACKGROUND
  Intact parathyroid hormone (PTH) tests are frequently sandwich immunoassays. Enzymes that cleave PTH may cause falsely lower PTH results. The objective of this study was to determine whether bovine thrombin in Becton Dickinson (BD) Vacutainer rapid serum tubes™ (RSTs) may lead to PTH results that are lower than in plasma separator tube™ (PST) or serum separator tube™ (SST) collections.
  
  
  METHODS
  Tubes of blood (PST, SST, and RST) were collected from donors. PTH concentrations were measured on a Roche Cobas e602 analyzer in aliquots held at room temperature or 4°C across time. Instrument comparison studies were also conducted on an Abbott Architect i1000SR and a Siemens Immulite 2000 XPi. Previously collected serum specimens were also incubated in exogenous bovine thrombin, the direct thrombin inhibitor hirudin, or both. Freshly collected RST specimens were also spiked with hirudin after clotting and centrifugation.
  
  
  RESULTS
  Significant decreases in PTH degradation rate constants were observed according to tube type, with degradation rates faster in RSTs than SSTs, and SSTs faster than PSTs. PTH degradation rate was temperature dependent. PTH decreases induced by exogenous bovine thrombin, as well as endogenous human thrombin, were reduced by hirudin.
  
  
  CONCLUSIONS
  Bovine thrombin is responsible for the decrease in PTH results observed in RSTs. Endogenous human thrombin, activated during clot formation, is likely responsible for the smaller decreases observed in non-RST sera versus plasma.
authors.affiliation: ARUP Institute for Clinical and Experimental Pathology, 500 Chipeta Way, Salt Lake City, UT 84108, USA.
authors.forename: Sonia L
authors.initials: SL
authors.lastname: La'ulu
authors.affiliation: Department of Pathology, University of Utah School of Medicine, 500 Chipeta Way, Salt Lake City, UT 84108, USA.
authors.forename: Joely A
authors.initials: JA
authors.lastname: Straseski
authors.affiliation: Department of Pathology, University of Utah School of Medicine, 15 N Medical Drive East, Salt Lake City, UT 84132, USA.
authors.forename: Robert L
authors.initials: RL
authors.lastname: Schmidt
authors.affiliation: Department of Pathology, University of Utah School of Medicine, 500 Chipeta Way, Salt Lake City, UT 84108, USA. Electronic address: jonathan.genzen@path.utah.edu.
authors.forename: Jonathan R
authors.initials: JR
authors.lastname: Genzen
mesh_terms: D000818:Animals; D000991:Antithrombins / Q000494:pharmacology; D001800:Blood Specimen Collection / Q000379:methods* / Q000592:standards; D002417:Cattle; D006629:Hirudins / Q000494:pharmacology; D006801:Humans; D010281:Parathyroid Hormone / Q000097:blood*; D013917:Thrombin / Q000037:antagonists & inhibitors* / Q000502:physiology*
chemical_list: D000991:Antithrombins; D006629:Hirudins; D010281:Parathyroid Hormone; D013917:Thrombin
keywords: blood collection tubes; interference; parathyroid hormone; plasma; serum; thrombin