PTH 1-84 and PTH "7-84" in the noninvasive diagnosis of renal bone disease.
BACKGROUND
The intact parathyroid hormone (PTH) assay evaluates levels of serum 1-84 PTH and other N-terminally truncated PTH fragments, mainly PTH "7-84." This PTH molecule has been found experimentally to interfere with biological activity of PTH 1-84, perhaps through its binding to the PTH receptor complex. Therefore, assuming that high levels of PTH 7-84 are a cause of bone resistance to PTH, it has been hypothesized that a decreased 1-84 to 7-84 PTH ratio caused by a relative increase in PTH 7-84 level might help in the noninvasive diagnosis of low-turnover osteodystrophy (LTO).


METHODS
This study was performed in 35 patients with chronic renal failure on hemodialysis therapy who underwent bone biopsy for a histological, histomorphometric, and histodynamic study. In addition, blood samples were obtained for intact PTH, 1-84 PTH, and total PTH assays. PTH 7-84 level was obtained from the difference between total and 1-84 PTH assay results.


RESULTS
Nine patients had LTO (8 patients, adynamic bone disease; 1 patient, osteomalacia), 12 patients had hyperparathyroidism (HP), and 14 patients had mixed osteodystrophy (MO). On average, 1-84 PTH levels were approximately 60% of mean values for intact PTH. The two assays were strictly correlated. Average 1-84 to 7-84 PTH ratios were 1.57 +/- 0.85, 1.73 +/- 1.31, and 1.95 +/- 2.1 in the three histological groups (LTO, HP, and MO, respectively), with no significant difference.


CONCLUSIONS
Contrary to previous expectations, results do not favor the hypothesis of a role of 7-84 PTH in bone resistance in renal osteodystrophy. The 1-84 to 7-84 PTH ratio is not a marker of LTO and is of no use in noninvasive histological diagnosis.
Coen
Giorgio
G
Department of Clinical Science, Second Medical Faculty, La Sapienza University, Rome, Italy. coen.gf@flashnet.it
Bonucci
Ermanno
E
Ballanti
Paola
P
Balducci
Alessandro
A
Calabria
Santo
S
Nicolai
Giulia A
GA
Fischer
Maria Stephanie
MS
Lifrieri
Francesca
F
Manni
Micaela
M
Morosetti
Massimo
M
Moscaritolo
Eleonora
E
Sardella
Daniela
D
D015415:Biomarkers / Q000097:blood; D012080:Chronic Kidney Disease-Mineral and Bone Disorder / Q000097:blood / Q000175:diagnosis*; D005260:Female; D006801:Humans; D006961:Hyperparathyroidism / Q000097:blood / Q000175:diagnosis; D007676:Kidney Failure, Chronic / Q000097:blood / Q000628:therapy; D008297:Male; D008875:Middle Aged; D010018:Osteomalacia / Q000097:blood / Q000175:diagnosis; D010281:Parathyroid Hormone / Q000097:blood*; D010446:Peptide Fragments / Q000097:blood*; D006435:Renal Dialysis / Q000379:methods
D015415:Biomarkers; D010281:Parathyroid Hormone; D010446:Peptide Fragments; C414937:parathyroid hormone (7-84)