title: Effect of a protease inhibitor on in vitro stability of intact parathyroid hormone.
abstract: BACKGROUND
  We investigated whether increased protease activity explains the increased in vitro degradation of intact parathyroid hormone (iPTH) observed in serum when compared to EDTA plasma.
  
  
  METHODS
  Pre-dialysis blood samples for iPTH were taken from 11 patients with chronic renal failure and collected into plain glass tubes, tubes containing 200 KIU/mL aprotinin (a protease inhibitor) and EDTA tubes. All sample aliquots were separated at 20 min, 1 h, 2 h, 4 h, 8 h and 24 h post collection.
  
  
  RESULTS
  Over 24 h, iPTH concentrations remained unchanged in EDTA tubes. iPTH concentrations were significantly lower in both plain tubes (P < 0.01) and aprotinin tubes (P < 0.001) at 24 h when compared to the baseline sample (20 min). At 24 h, iPTH concentrations in EDTA tubes were higher than in plain tubes (P < 0.001) and aprotinin tubes (P < 0.01). The addition of aprotinin to plain tubes significantly reduced the degradation of iPTH (P < 0.05) at 24 h.
  
  
  CONCLUSIONS
  Aprotinin significantly reduces the in vitro degradation of iPTH in plain tubes at 24 h from 24.7% to 9.6%. We suggest that increased protease activity contributes to the decline in serum iPTH over time. As this is observed in serum and not plasma it suggests that the increased protease activity may be due to the clotting process.
authors.affiliation: Department of Clinical Chemistry, New Cross Hospital, Wolverhampton, WV10 0PQ, UK. neil.anderson@rwh-tr.nhs.uk
authors.forename: N R
authors.initials: NR
authors.lastname: Anderson
authors.forename: J
authors.initials: J
authors.lastname: Nicholas
authors.forename: M R
authors.initials: MR
authors.lastname: Holland
authors.forename: R
authors.initials: R
authors.lastname: Gama
mesh_terms: D007611:Aprotinin / Q000494:pharmacology; D002624:Chemistry, Clinical / Q000379:methods; D003956:Dialysis; D004492:Edetic Acid / Q000494:pharmacology; D006801:Humans; D007676:Kidney Failure, Chronic / Q000097:blood; D010281:Parathyroid Hormone / Q000097:blood*; D011480:Protease Inhibitors / Q000494:pharmacology*; D013048:Specimen Handling; D013997:Time Factors
chemical_list: D010281:Parathyroid Hormone; D011480:Protease Inhibitors; D007611:Aprotinin; D004492:Edetic Acid