The Values of Osteopontin and Bone Specific Alkaline Phosphatase in Diagnosis of Osteoporosis. AComparative Study

Abstract

Dual-energy X-ray absorptiometry (DXA) is commonly used for diagnosis of osteoporosis, but it has its limitations. Bone turnover markers have advantages over DXA as they are cheap, non-invasive and can detect changes in bone turnover rates earlier. However, they do have disadvantages, particularly high within- and between-patient variability. The ability of bone turnover markers to predict of osteoporosis has yet to be established. The objective of this study is to assess the use of bone markers for diagnosis of osteoporosis in postmenopausal women and compare the results with those obtained by DXA method. This case- control study was conducted between October 2012 and April 2014. Forty-four postmenopausal osteoporotic women and forty-four healthy women as a control group, aged between 50-65 years old were involved in this study. They were recruited from the Al-Yarmouk Teaching Hospital, Baghdad, Iraq, and selected on the basis of inclusion and exclusion criteria. The physical characteristics were assessed using anthropometric measurements including height, weight, and body mass index (BMI). Bone mineral density (BMD) of lumbar and hipwere measured by the dual-energy X-ray absorptiometry (DXA) instrument. Serum Calcium and Phosphorous were measured using spectrophotometric kit while serum levels of osteopontin and bone specific alkaline phosphatase were measured by Enzyme-Link Immune Sorbent Assay (ELISA).Receiver operator characteristic (ROC) curves were constructed to plot sensitivity against specificity of lumbar and hip BMD, OPN and BAP levels as diagnosis tests for osteoporosis. The areas under the ROC curves (AUC) were calculated and compared with the AUC (0.5) of the non-diagnostic test (the line with slope of 1).The osteoporotic postmenopausal women had higher mean serum OPN and BAP levels compared to the healthy women (16.41 ± 6.33 vs 7.13 ± 5.88 ng/mL; P < 0.01); ( 47.08 ± 36.47 vs 24.42 ± 16.86; P < 0.01), respectively. When using a OPN concentration of 13.25 ng/ml as a cut off value for the diagnosis of osteoporosis sensitivity was 81.8%, specificity 86.4% and when using a BAP concentration of 31.05 ng/ml as a cut off value sensitivity was 81.8%, specificity 86.4%, Where is the sensitivity of lumbar and hipBMD was 100%, specificity 100% as a cut off value 0.925 g/cm2and 0.785 g/cm2respectively. There were no significant differences in mean values of Ca+2and P (p>0.05).The DXA is a more valid and reliable tool to utilize in diagnosis of osteoporosisin postmenopausal women than the measurement of serum OPN and BAP level.