Abstract
ObjectiveWe undertook to identify levels for plasma β isomerised carboxy-terminal telopeptides of type I collagen (p-βCTX-I) that are comparable to currently used urine amino-terminal telopeptides of type I collagen (u-NTX) cut-points and treatment targets in osteoporosis. Design and methodsFasting morning samples were collected from patients attending tertiary hospitals and clinics for investigation of metabolic bone disease. Patients with Paget's disease or <20years of age were excluded. Second void spot urine for NTX and plasma (EDTA) samples were utilised. Urine was analysed routinely and plasma stored at −20C until analysis by enzyme-linked immunosorbent assay (ELISA) (Immunodiagnostic Systems plc), E170 (Roche Diagnostics) and IDS-iSYS (Immunodiagnostic Systems plc) methods. The relationship of u-NTX with each p-βCTX-I method's results was assessed by Passing and Bablok regression, and p-βCTX-I levels equivalent to u-NTX cut-points and targets were interpolated. ResultsOne hundred and forty six patients were included. Spearman correlation coefficients ranged from 0.71 to 0.75 for the three βCTX-I assays. The equivalent βCTX-I concentrations for NTX/Cr values of 21 (fracture risk reduction target following risedronate therapy), 27 (healthy pre-menopausal women's mean value), and 38 (threshold for reduction of BMD on calcium alone) nmol BCE/mmol were 230, 312 and 462ng/L for the automated Roche assay and 271, 395 and 624ng/L for the automated IDS i-SYS assay respectively. ConclusionsThe p-βCTX-I equivalent to the only available fracture outcome based absolute treatment threshold of 21nmol BCE/mmol established for u-NTX, is close to 250ng/L but will vary between p-βCTX-I assays.
Published Version
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