Similar predictive value of bone turnover using first- and second-generation immunometric PTH assays in pediatric patients treated with peritoneal dialysis.
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.
Salusky
Isidro B
IB
Division of Pediatric Nephrology, Department of Pediatrics, David Geffen School of Medicine at UCLA, Los Angeles, California, USA. isalusky@mednet.ucla.edu
Goodman
William G
WG
Kuizon
Beatriz D
BD
Lavigne
Jeffrey R
JR
Zahranik
Richard J
RJ
Gales
Barbara
B
Wang
He-Jing
HJ
Elashoff
Robert M
RM
Jüppner
Harald
H
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
D010281:Parathyroid Hormone