Osteocalcin, also referred to as bone G1a protein, is a protein produced by the osteoblasts and dentin and has a function in bone mineralization and calcium ion homeostasis. A small amount of osteocalcin, an integral part in bone formation, is released into the blood and therefore can serve as a marker for recent bone formation. Osteocalcin levels are influenced by age (rapid growth) and gender (males somewhat higher) and are increased during menopause.
This test is used to screen for osteoporosis in postmenopausal women, assess risk for fractures, and determine eligibility for treatment for osteoporosis. The U.S. Preventive Task Force recommends screening for osteoporosis in women older than 65 years and in women younger than 65 years who have a risk of fracture that is equal to or greater than that of a 65-year-old White woman. Screening is not recommended for men. Osteocalcin is a specific marker for bone formation and is regulated by 1,25-dehydroxyvitamin D.
Osteocalcin: 8.1 ± 4.6 μg/L or 1.4 ± 0.8 nmol/L
Carboxylated osteocalcin: 9.9 ± 0.5 μg/L or 1.7 ± 0.1 nmol/L
Undercarboxylated osteocalcin: 3.7 ± 1.0 μg/L or 0.6 ± 0.2 nmol/L
Normal Using RIA:
Adult male: 3.0–13.0 ng/mL or 3.0–13.0 μg/L
Premenopausal female: 0.4–8.2 ng/mL or 0.4–8.2 μg/L
Postmenopausal female: 1.5–11.0 ng/mL or 1.5–11.0 μg/L
There is a diurnal variation, a peak during the night and a decrease in the morning.
Collect a venous blood sample of serum on ice, separate within 1 hour, and immediately freeze. Avoid a freeze–thaw cycle.
Abnormally increased levels indicate increased bone turnover in persons with hyperparathyroidism, fractures, and acromegaly.
Decreased levels are associated with hypoparathyroidism, a deficiency of GH, multiple myeloma, cirrhosis of the liver, and medications such as glucocorticoids, bisphosphonates, and calcitonin.
Pretest Patient Care
Explain purpose and procedure of test. Record age and menopausal state. Tell the patient that the risk for osteoporosis increases steadily with age. Also, obtain pertinent personal and family history of osteoporotic fractures, history of falls, and so forth.
Follow Chapter 1 guideline for safe, effective, informed pretest care.
Posttest Patient Care
Review test outcomes, report and record findings, and counsel regarding further tests (e.g., dual-energy x-ray absorptiometry, bone density of the femoral neck, or quantitative ultrasound) and possible treatment (e.g., medical: alendronate, raloxifene). Sixteen percent of postmenopausal women will be found to have lumbar spine osteoporosis. Other blood test markers of bone resorption include pyridinolines, telopeptides, acid phosphatase, and urine tests of hydroxyproline and galactosyl hydroxylysine. These markers are known as collagen cross-links. Modify the nursing care plan as needed.
See Chapter 1 for safe, effective, informed posttest care.