title: Similar predictive value of bone turnover using first- and second-generation immunometric PTH assays in pediatric patients treated with peritoneal dialysis.
abstract: BACKGROUND
  Accurate measurements of the concentration of parathyroid hormone (PTH) in serum or plasma are essential for the proper assessment of renal osteodystrophy. The first-generation immunometric PTH assay (1st PTH-IMA) not only detects the intact hormone, but also additional PTH fragments truncated at the amino N-terminally truncated PTH-derived fragments [ntPTH(1-84)]. A second-generation immunometric PTH assay (2nd PTH-IMA) recognizes only PTH(1-84) and possibly PTH fragments that are truncated at the carboxyl-terminus but not PTH(7-84). Whether estimates of the ratio between PTH(1-84) and ntPTH(1-84) fragments are a better predictor of bone turnover remains controversial.
  
  
  METHODS
  Thirty-three patients aged 12.8 +/- 4.4 years treated with continuous cycling peritoneal dialysis (CCPD) for 13 +/- 9 months underwent iliac crest bone biopsy. PTH levels were measured by two newly developed first-generation and second-generation PTH-IMA. The ntPTH(1-84) fragments were calculated by subtracting PTH values determined using the 2nd PTH-IMA from values obtained using 1st PTH-IMA that detects both PTH(1-84) and relatively large ntPTH(1-84).
  
  
  RESULTS
  Determinations of PTH levels by both assays were highly correlated (r = 0.89, P < 0.001). The relationships between first-generation and second-generation PTH-IMA and bone formation were similar (r = 0.67, P < 0.0001 and r = 0.64, P < 0.0001, respectively). When patients were grouped according to the presence or absence of secondary hyperparathyroidism, the ratio PTH(1-84) to ntPTH(1-84) did not differ between groups.
  
  
  CONCLUSIONS
  PTH concentrations determined by either the first- or the second-generation PTH-IMA were found to be better predictors of bone formation than the PTH(1-84) to ntPTH(1-84) fragments ratio.
authors.affiliation: Division of Pediatric Nephrology, Department of Pediatrics, David Geffen School of Medicine at UCLA, Los Angeles, California, USA. isalusky@mednet.ucla.edu
authors.forename: Isidro B
authors.initials: IB
authors.lastname: Salusky
authors.forename: William G
authors.initials: WG
authors.lastname: Goodman
authors.forename: Beatriz D
authors.initials: BD
authors.lastname: Kuizon
authors.forename: Jeffrey R
authors.initials: JR
authors.lastname: Lavigne
authors.forename: Richard J
authors.initials: RJ
authors.lastname: Zahranik
authors.forename: Barbara
authors.initials: B
authors.lastname: Gales
authors.forename: He-Jing
authors.initials: HJ
authors.lastname: Wang
authors.forename: Robert M
authors.initials: RM
authors.lastname: Elashoff
authors.forename: Harald
authors.initials: H
authors.lastname: Jüppner
mesh_terms: D000293:Adolescent; D016723:Bone Remodeling / Q000502:physiology; D002648:Child; D012080:Chronic Kidney Disease-Mineral and Bone Disorder / Q000097:blood / Q000175:diagnosis* / Q000209:etiology; D005260:Female; D006801:Humans; D007118:Immunoassay / Q000379:methods*; D007676:Kidney Failure, Chronic / Q000150:complications* / Q000628:therapy; D008297:Male; D010281:Parathyroid Hormone / Q000032:analysis* / Q000097:blood*; D010530:Peritoneal Dialysis; D011237:Predictive Value of Tests; D012680:Sensitivity and Specificity
chemical_list: D010281:Parathyroid Hormone