title: Intact PTH assay overestimates true 1-84 PTH levels after maxacalcitol therapy in dialysis patients with secondary hyperparathyroidism.
abstract: BACKGROUND
  Although the so-called intact parathyroid hormone (iPTH) assay detects not only true 1-84 PTH (1-84PTH) but also large C-terminal PTH fragments, it remains inconclusive whether the 1-84PTH assay is more useful in clinical practice. Previous studies have shown that the results of these two PTH assays in dialysis patients are closely correlated.
  
  
  METHODS
  Chronic dialysis patients whose plasma iPTH levels were >400 pg/ml were selected for inclusion in the present study. Following a 4 week wash-out time during which all vitamin D administration was halted, maxacalcitol was intravenously injected at the end of dialysis sessions three times per week for 24 weeks, at an initial dosage of 10 micro g.
  
  
  RESULTS
  Ninety-seven patients with secondary hyperparathyroidism were included in our analysis. Their serum calcium levels were elevated from the start levels while phosphate levels remained unchanged. The plasma 1-84PTH levels constantly declined throughout the 24 weeks. Although the patients' plasma 1-84PTH and iPTH levels were closely correlated with each other both at the beginning of the study and after 24 weeks of maxacalcitol therapy, the ratio of 1-84PTH/iPTH consistently decreased throughout the study period (P<0.01). The changes in the ratio were significantly correlated with changes in serum calcium levels.
  
  
  CONCLUSIONS
  Twenty-four weeks of intravenous maxacalcitol injection therapy significantly reduced the 1-84PTH/iPTH ratio. Estimated 1-84PTH levels from iPTH levels using a conversion formula obtained before the treatment were 21.0+/-20.4% higher than measured 1-84PTH levels after the therapy. Thus, iPTH measurement has a potential risk to overestimate 1-84PTH levels when evaluating the efficacy of maxacalcitol therapy in dialysis patients with secondary hyperparathyroidism.
authors.affiliation: FJSIM, Division of Intensive Care Medicine, Niigata University Medical Hospital, 1-754 Asahimachi-Dori, Niigata, Niigata 951-8510, Japan. jjkaz@med.niigata-u.ac.jp
authors.forename: Junichiro J
authors.initials: JJ
authors.lastname: Kazama
authors.forename: Kentaro
authors.initials: K
authors.lastname: Omori
authors.forename: Noboru
authors.initials: N
authors.lastname: Higuchi
authors.forename: Naoki
authors.initials: N
authors.lastname: Takahashi
authors.forename: Yumi
authors.initials: Y
authors.lastname: Ito
authors.forename: Hiroki
authors.initials: H
authors.lastname: Maruyama
authors.forename: Ichiei
authors.initials: I
authors.lastname: Narita
authors.forename: Thomas L
authors.initials: TL
authors.lastname: Cantor
authors.forename: Ping
authors.initials: P
authors.lastname: Gao
authors.forename: Fumitake
authors.initials: F
authors.lastname: Gejyo
mesh_terms: D002117:Calcitriol / Q000031:analogs & derivatives / Q000627:therapeutic use*; D005260:Female; D006801:Humans; D006980:Hyperthyroidism / Q000097:blood* / Q000188:drug therapy*; D008297:Male; D008875:Middle Aged; D010281:Parathyroid Hormone / Q000097:blood*; D011446:Prospective Studies; D006435:Renal Dialysis; D015203:Reproducibility of Results
chemical_list: D010281:Parathyroid Hormone; D002117:Calcitriol; C051883:maxacalcitol