The PTH-(1-84)/C-PTH fragment ratio predicts bone turnover with acceptable precision for biological measurements. Moreover, a change in serum calcium levels is one of the regulators of the relative amount of circulating PTH-(1-84) and its large C-PTH fragments.

In conclusion, the Z-score at the mid-radius was decreased in HD patients and correlated with high serum PTH but not with fractures. Bone fractures were associated with the time passed on HD and with a low total body Z-score. Rib fractures were frequent and associated with a poor nutritional state.

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Background and objectives Use of bone mineral density (BMD) by dual-energy x-ray absorptiometry (DXA) is controversial for diagnosing bone loss in CKD patients on dialysis. The alternative quantitative computed tomography (QCT) is expensive and requires high radiation exposure. This study compared the two techniques and evaluated serum biochemical parameters for prediction of bone loss.Design, setting, participants, & measurements This prospective study enrolled patients from dialysis centers throughout Kentucky. BMD of the spine and hip was measured at baseline and after 1 year by DXA and QCT. Customary and novel serum biochemical parameters were obtained at the same times, including calcium, phosphorus, whole and intact parathyroid hormone, bone-specific alkaline phosphatase, procollagen type 1 N-terminal propeptide, tartrate-resistant acid phosphatase-5b, Dickkopf-1, fibroblast growth factor, and sclerostin. Rates of detection of osteoporosis by DXA and QCT were compared. Correlations were calculated between baseline biochemical parameters and BMD at baseline and changes over 1 year. Multivariable regression was performed to adjust for age, sex, body mass index, and race.Results Eighty-one patients completed the study (mean age=52.6612.3 years, 56% men, 53% African American, and median dialysis vintage=41 months). At baseline, QCT and DXA of the spine identified similar rates of osteoporosis (13.6% and 13.6%), but at the hip, DXA identified more osteoporosis (22.2% versus 13.6%). At any site and by either method, 33.3% of the patients were osteoporotic. Baseline BMD correlated with sclerostin, intact parathyroid hormone, bone-specific alkaline phosphatase, tartrate-resistant acid phosphatase-5b, and fibroblast growth factor. At 1 year, hip QCT identified a higher number of patients experiencing bone loss (51.3%) than DXA (38.5%). After multivariable adjustment, baseline sclerostin and tartrate-resistant acid phosphatase-5b predicted bone loss measured by QCT of the hip; procollagen type 1 N-terminal propeptide predicted cortical spine bone gain by QCT.Conclusions QCT identified prospectively more bone loss at the hip than DXA. The baseline serum biochemical parameters sclerostin and tartrate-resistant acid phosphatase-5b were noninvasive independent predictors of bone loss in CKD patients on dialysis.

In 8 adolescents with end-stage renal disease (ESRD), basal PTH concentrations measured with a novel immunoradiometric assay (IRMA) (Scantibodies Laboratory, Inc.; S-IRMA) were invariably lower than those estimated with an established assay (Nichols Institute; N-IRMA) (263 +/- 228 versus 645 +/- 442 pg/ml, respectively; p<0.00001). During in vivo dynamic testing, set points for calcium-regulated PTH release were indistinguishable for both IRMAs (1.21 +/- 0.05 versus 1.22 +/- 0.06). However, maximal PTH concentrations were significantly lower when measured by S-IRMA then by N-IRMA (557 +/- 448 and 1114 +/- 606 pg/ml, respectively); minimum PTH concentrations were 41 +/- 65 pg/ml (5.0 +/- 4.2% of maximum) and 189 +/- 137 pg/ml (13.6 +/- 7.2% of maximum), respectively. Correlation between PTH and blood ionized calcium indicated that PTH measured by S-IRMA decreased more readily than the concentrations determined by N-IRMA. The N-IRMA showed indistinguishable cross-reactivity with hPTH(1-84) and hPTH(7-84), while the S-IRMA detected only the full-length peptide. Furthermore, the radiolabeled detection antibody of the N-IRMA interacted equivalently with hPTH(1-34) and hPTH(2-34), while the S-IRMA showed crossreactivity only with hPTH(1-34). These differences in assay specificity could explain the observed differences in ESRD, and suggest that PTH concentrations estimated by the S-IRMA reflect more accurately the amount of biologically active PTH in the circulation. Since low concentrations of PTH are frequently associated with adynamic bone disease, our findings may have significant implications for the treatment of renal osteodystrophy with calcium and/or biologically active vitamin D analogs.