Correlation of Serum Osteocalcin Fractions with Bone Mineral Density in Women During the First 10 Years after Menopause

Abstract.

Serum immunoreactive osteocalcin (irOC) consists of two fractions that differ from each other by their affinity for hydroxyapatite. The high and low affinity fractions are referred to as irOC_bound and irOC_free, respectively. To evaluate whether these fractions are determinants for different characteristics of bone or bone metabolism, we have performed a cross-sectional study among 212 apparently healthy women between 20 and 90 years of age. Bone mineral density (BMD) was determined at the lumbar spine, and the right femur neck, trochanter, and Ward's triangle using dual-energy X-ray absorptiometry (DXA). Biochemical markers for bone formation and resorption were determined in serum and in urine. After classification according to menopausal age, an inverse correlation was found in the 1–10 years postmenopausal women between irOC_free and BMD, notably of the Ward's triangle and femur neck. It is concluded that in 1–10 years postmenopausal women, irOC_free is an independent marker for BMD, but that in other age groups the association is less clear or is absent.