Specific measurement of PTH (1-84) in various forms of renal osteodystrophy (ROD) as assessed by bone histomorphometry.
BACKGROUND
Parathyroid hormone (PTH) measurements serve as a noninvasive, diagnostic tool for the assessment of renal osteodystrophy (ROD). Their value has been questioned following reports indicating that all commercially available intact PTH (I-PTH) assays cross-react with amino terminally truncated PTH fragments. Because these fragments can account for 50% of total PTH, their detection will overestimate the true PTH concentration and may lead to diagnostic inaccuracies. The aim of this study was to evaluate the specific Bio-Intact PTH (1-84) Assay (BI-PTH) in patients with various types of ROD confirmed by bone biopsy.


METHODS
Bone biopsies were taken from 132 patients with chronic kidney disease (CKD) stages 3 to 5, and quantitative bone histomorphometry was done. Plasma PTH levels were measured using both the BI-PTH and I-PTH assays on an automated analyzer.


RESULTS
Patients with CKD stages 3/4 and low turnover skeletal lesions had BI-PTH values (pg/mL, mean +/- SD) of 35 (+/-34) and I-PTH values of 59 (+/- 63). Corresponding values for BI-PTH and I-PTH in those with high turnover lesions were 141 (+/-60) and 221 (+/-106). Patients with CKD stage 5 and low turnover skeletal lesions had BI-PTH and I-PTH levels of 51 (+/-38) and 90 (+/-60), respectively, whereas the corresponding results for BI-PTH and I-PTH in those with high turnover lesions were 237 (+/-214) and 461 (+/-437). The areas under the receiver operating characteristic (ROC) curves for distinguishing low turnover from high turnover lesions were 0.94 for BI-PTH and 0.91 for I-PTH in CKD stages 3/4 and 0.86 for BI-PTH and 0.85 for I-PTH in CKD stage 5. Among all patients, BI-PTH levels are approximately 50% lower than I-PTH levels, but the results of the two assays are correlated highly (R2 = 0.92).


CONCLUSIONS
Plasma PTH measurements using either the BI-PTH or I-PTH assay effectively identify patients with reduced bone turnover and serve to distinguish this subgroup from those with high turnover lesions of renal bone disease. Both assays provide better diagnostic discrimination for this purpose than calculated values for the ratio of PTH (1-84)/amino terminally truncated PTH fragments.
Lehmann
Gabriele
G
Division of Rheumatology and Osteology, Department of Internal Medicine III, Friedrich-Schiller University of Jena, Jena, Germany. gabriele.lehmann@med.uni-jena.de
Stein
Günter
G
Hüller
Manfred
M
Schemer
Rudolf
R
Ramakrishnan
Kastooriranganathan
K
Goodman
William G
WG
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D015415:Biomarkers / Q000097:blood; D001706:Biopsy; D001842:Bone and Bones / Q000473:pathology*; D012080:Chronic Kidney Disease-Mineral and Bone Disorder / Q000097:blood* / Q000473:pathology*; D005260:Female; D006801:Humans; D007118:Immunoassay / Q000379:methods; D007676:Kidney Failure, Chronic / Q000097:blood / Q000150:complications; D008297:Male; D008875:Middle Aged; D010281:Parathyroid Hormone / Q000097:blood*; D010446:Peptide Fragments / Q000097:blood*; D012680:Sensitivity and Specificity
D015415:Biomarkers; D010281:Parathyroid Hormone; D010446:Peptide Fragments