Biological variation and reference intervals for circulating osteopontin, osteoprotegerin, total soluble receptor activator of nuclear factor kappa B ligand and high‐sensitivity C‐reactive protein

Abstract

Objective. Monitoring inflammatory diseases and osteoclastogenesis with osteopontin (OPN), osteoprotegerin (OPG), total soluble receptor activator of nuclear factor kappa B ligand (total sRANKL) and high‐sensitivity C‐reactive protein (hsCRP) has recently attracted increased interest. The purpose of our study was to determine reference intervals, variability caused by sampling time, biological variation and stability after repeated freeze–thaw cycles of circulating levels of OPN, OPG, total sRANKL and hsCRP. Material and methods. Plasma OPN and plasma OPG concentrations were determined with sandwich ELISA; serum total sRANKL concentration was determined using a two‐site sandwich ELISA; and hsCRP was analysed by turbidimetry in 300 Danish blood donors (183 M and 117 F) with a median age of 43 years (range 18–64 years). Variability due to biological variation and sampling time was studied in serial samples from 38 healthy subjects. Results. The 95th percentiles in the donors were 76 µg/L for OPN, 4.2 pmol/L for OPG, 40.2 nmol/L for total sRANKL and 12 mg/L for hsCRP. The overall medians for both genders were 51 µg/L, 2.2 pmol/L, 0.66 nmol/L and 1.0 mg/L, respectively. We found a significant correlation between hsCRP and OPN (rho = 0.173; p<0.003). The biological within‐subject variations were calculated to be 8.2 % for OPN, 8.8 % for total sRANKL and 50 % for hsCRP. Conclusions. Reference intervals have been established with a high analytic performance for OPN and an acceptable analytic performance for OPG and total sRANKL. The study revealed low biological variation for OPN and total sRANKL and high biological variation for hsCRP.

• Blood donors
• ELISA
• inter‐observer variation
• intra‐observer variation
• quality control

Acknowledgements

We thank for technical assistants from laboratory technicians, V. Myrhøj, A. Quist, J. Nymann and Ortho‐Clinical Diagnostics, Johnson & Johnson for providing high sensitive C‐reactive protein kits. We also thank the powers that be at the blood banks of Hvidovre University Hospital and Rigshospitalet, Copenhagen University Hospital for supplying blood, and H. Ytting and C. Frederiksen in the Department of Surgical Gastroenterology, Hvidovre Hospital, for assistance in collecting the blood samples. The study was partly supported through grants from the Danish Rheumatism Association, the A. P. Møller Foundation for the Advancement of Medical Science, the Danish Hospital Foundation for Medical Research, Region of Copenhagen, the Faroe Islands and Greenland, the Hørslev Foundation, the Jacob Madsen and Olga Madsen Foundation, the Aase and Ejnar Danielsen Foundation, the Øster‐Jørgensen Foundation, the Rømhild Andersen Foundation and the Danish Cancer Society (HJN is Danish Cancer Society Professor of Surgical Oncology).