Parathyroid hormone and its fragments in children with chronic renal failure.
Parathyroid hormone (PTH) immunoradiometric assays (IRMA) exhibit cross-reactivity between 1-84 PTH and long carboxyl-terminal-PTH (C-PTH) molecules. C-PTH antagonizes the biological actions of 1-84 PTH and circulates in excess in chronic renal failure (CRF), partially explaining why supra-physiological PTH levels are recommended to maintain bone turnover. Furthermore, the ratio 1-84 PTH/C-PTH may be related to bone turnover. This study characterizes the 1-84 PTH/C-PTH ratio in children with varying severity of CRF and levels of PTH. Two hundred and forty-one children with CRF, managed with the aim of preventing the development of hyperparathyroidism, had PTH measured by 'intact' IRMA and a new more specific Cyclase-Activating-PTH (CAP) IRMA. C-PTH levels were calculated by subtracting CAP-IRMA from 'intact' IRMA. Fifty-three controls with normal renal function were also recruited. Mean 'intact' IRMA correlated with CAP-IRMA ( r=0.98), but was higher ( P<0.001). The mean 1-84 PTH/C-PTH ratio was lower than controls in dialysis patients ( P=0.022) and those with a glomerular filtration rate <30 ml/min per m(2 )( P=0.033). This ratio was comparable to controls when the PTH level was normal, but was lower with PTH levels outside the normal range ( P<0.01). These data suggest that CAP-IRMA gives a more accurate assessment of actual PTH levels than 'intact' IRMA in CRF. Maintenance of normal PTH levels throughout the course of CRF permits the maintenance of a normal 1-84 PTH/C-PTH ratio, the clinical significance of which requires further investigation in children.
Department of Nephro-Urology, Institute of Child Health and Great Ormond Street Hospital for Children NHS Trust, London, UK. s.waller@doctors.org.uk
Simon
S
Waller
Anthony
A
Reynolds
Deborah
D
Ridout
Tom
T
Cantor
Ping
P
Gao
Lesley
L
Rees
D002648:Child; D002675:Child, Preschool; D005260:Female; D005919:Glomerular Filtration Rate; D006801:Humans; D007676:Kidney Failure, Chronic / Q000097:blood* / Q000503:physiopathology; D007677:Kidney Function Tests; D008297:Male; D010281:Parathyroid Hormone / Q000097:blood*; D010446:Peptide Fragments / Q000097:blood; D011863:Radioimmunoassay; D012016:Reference Values
D010281:Parathyroid Hormone; D010446:Peptide Fragments