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Similar predictive value of bone turnover using first- and second-generation immunometric PTH assays in pediatric
Isidro B Salusky1, William G Goodman, Beatriz D Kuizon
1Division of Pediatric Nephrology, Department of Pediatrics, David Geffen School of Medicine at UCLA, Los Angeles, California, USA. isalusky@mednet.ucla.edu
Insights
Accurate parathyroid hormone (PTH) measurements are crucial for assessing renal osteodystrophy. Both first- and second-generation PTH assays predict bone formation better than PTH fragment ratios.
Area of Science:
- Nephrology
- Endocrinology
- Bone Metabolism
Background:
- Accurate parathyroid hormone (PTH) measurement is vital for assessing renal osteodystrophy.
- First-generation PTH assays detect intact PTH and N-terminally truncated fragments (ntPTH(1-84)).
- Second-generation PTH assays primarily detect intact PTH(1-84).
Purpose of the Study:
- To evaluate the predictive value of PTH(1-84) to ntPTH(1-84) fragment ratios for bone turnover.
- To compare the efficacy of first- and second-generation PTH assays in assessing bone formation.
Main Methods:
- Thirty-three pediatric patients on continuous cycling peritoneal dialysis (CCPD) underwent iliac crest bone biopsy.
- PTH levels were measured using first- and second-generation PTH immunometric assays (IMA).
- N-terminally truncated PTH fragments (ntPTH(1-84)) were calculated by subtracting second-generation from first-generation assay values.
Main Results:
- PTH levels measured by both assays showed high correlation (r = 0.89, P < 0.001).
- Both first- and second-generation PTH-IMA showed similar strong correlations with bone formation (r = 0.67 and r = 0.64, respectively; P < 0.0001).
- The ratio of PTH(1-84) to ntPTH(1-84) did not differ between patient groups with or without secondary hyperparathyroidism.
Conclusions:
- PTH concentrations measured by either first- or second-generation PTH-IMA are superior predictors of bone formation.
- The ratio of PTH(1-84) to ntPTH(1-84) fragments is not a better predictor of bone formation than direct PTH measurements.
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.
Conclusion:
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.
