BGP

Abbreviation for bone Gla protein.

BGLAP

A gene on chromosome 1q25-q31 that encodes a protein which constitutes 1–2% of bone protein, which binds strongly to apatite and calcium.

Osteocalcin

Synonym/acronym: Bone GLA protein, BGP.

Common use

To assist in assessment of risk for osteoporosis and to evaluate effectiveness of therapeutic interventions.

Specimen

Serum (1 mL) collected in a red-top tube. Serum from a gold-, red/gray-top tube; plasma from a lavender (EDTA)-pink (K2EDTA), or green (sodium or lithium heparin)-top tube is also acceptable.

Normal findings

(Method: Electrochemiluminescence)

Age and Sex	Conventional Units	SI Units (Conventional Units × 1)
6 mo–6 yr
Male	39–121 ng/mL	39–121 mcg/L
Female	44–130 ng/mL	44–130 mcg/L
7–9 yr
Male	66–182 ng/mL	66–182 mcg/L
Female	73–206 ng/mL	73–206 mcg/L
10–12 yr
Male	85–232 ng/mL	85–232 mcg/L
Female	77–262 ng/mL	77–262 mcg/L
13–15 yr
Male	70–336 ng/mL	70–336 mcg/L
Female	33–222 ng/mL	33–222 mcg/L
16–17 yr
Male	43–237 ng/mL	43–237 mcg/L
Female	24–99 ng/mL	24–99 mcg/L
Adult
Male	3–40 ng/mL	3–40 mcg/L
Female
Premenopausal	5–30 ng/mL	5–30 mcg/L
Postmenopausal	9–50 ng/mL	9–50 mcg/L

Description

Osteocalcin is an important bone cell matrix protein and a sensitive marker in bone metabolism. It is produced by osteoblasts during the matrix mineralization phase of bone formation and is the most abundant noncollagenous bone cell protein. Synthesis of osteocalcin is dependent on vitamin K and vitamin D. Osteocalcin levels parallel alkaline phosphatase levels. Osteocalcin levels are affected by a number of factors, including estrogen levels. Assessment of osteocalcin levels permits indirect measurement of osteoblast activity and bone formation. Because it is released into the bloodstream during bone resorption, there is some speculation as to whether osteocalcin might also be considered a marker for bone matrix degradation and turnover.

This procedure is contraindicated for

N/A

Indications

Assist in the diagnosis of bone cancer
Evaluate bone disease
Evaluate bone metabolism
Monitor effectiveness of estrogen replacement therapy

Potential diagnosis

Increased in

Adolescents undergoing a growth spurt (levels in the blood increase as the rate of bone formation increases)
Chronic renal failure (related to accumulation in circulation due to decreased renal excretion)
Hyperthyroidism (primary and secondary) (related to increased bone turnover)
Metastatic skeletal disease (levels in the blood increase as bone destruction releases it into circulation)
Paget’s disease (levels in the blood increase as bone destruction releases it into circulation)
Renal osteodystrophy (related to bone degeneration secondary to hyperparathyroidism of chronic renal failure)
Some patients with osteoporosis (levels in the blood increase as bone destruction releases it into circulation)

Decreased in

(bone mineralization is stimulated by growth hormone)

(increased demand by developing fetus results in an increase in maternal bone resorption)

(related to increased bone loss)

Critical findings

N/A

Interfering factors

Drugs that may increase osteocalcin levels include anabolic steroids, calcitonin, calcitriol, danazol, nafarelin, pamidronate, parathyroid hormone, and stanozolol.
Drugs that may decrease osteocalcin levels include alendronate, antithyroid therapy, corticosteroids, cyproterone, estradiol valerate, estrogen/progesterone therapy, glucocorticoids, hormone replacement therapy, methylprednisolone, oral contraceptives, pamidronate, parathyroid hormone, prednisolone, prednisone, raloxifene, tamoxifen, and vitamin D.

Nursing Implications and Procedure

Pretest

Positively identify the patient using at least two unique identifiers before providing care, treatment, or services.
Patient Teaching: Inform the patient this test can assist in evaluating for bone disease.
Obtain a history of the patient’s complaints, including a list of known allergens, especially allergies or sensitivities to latex.
Obtain a history of the patient’s musculoskeletal system, symptoms, and results of previously performed laboratory tests and diagnostic and surgical procedures.
Note any recent procedures that can interfere with test results.
Obtain a list of the patient’s current medications, including herbs, nutritional supplements, and nutraceuticals (see Effects of Natural Products on Laboratory Values).
Review the procedure with the patient. Inform the patient that specimen collection takes approximately 5 to 10 min. Address concerns about pain and explain that there may be some discomfort during the venipuncture.
Sensitivity to social and cultural issues, as well as concern for modesty, is important in providing psychological support before, during, and after the procedure
Note that there are no food, fluid, or medication restrictions unless by medical direction.

Intratest

Potential complications: N/A
Avoid the use of equipment containing latex if the patient has a history of allergic reaction to latex.
Instruct the patient to cooperate fully and to follow directions. Direct the patient to breathe normally and to avoid unnecessary movement.
Observe standard precautions, and follow the general guidelines in Patient Preparation and Specimen Collection. Positively identify the patient, and label the appropriate specimen container with the corresponding patient demographics, initials of the person collecting the specimen, date, and time of collection. Perform a venipuncture.
Remove the needle and apply direct pressure with dry gauze to stop bleeding. Observe/assess venipuncture site for bleeding or hematoma formation and secure gauze with adhesive bandage.
Promptly transport the specimen to the laboratory for processing and analysis.

Post-Test

Inform the patient that a report of the results will be made available to the requesting health-care provider (HCP), who will discuss the results with the patient.
Nutritional Considerations: Increased osteocalcin levels may be associated with skeletal disease. Nutritional therapy is indicated for individuals identified as being at high risk for developing osteoporosis. Educate the patient regarding the National Osteoporosis Foundation’s guidelines, which include a regular regimen of weight-bearing exercises, limited alcohol intake, avoidance of tobacco products, and adequate dietary intake of vitamin D and calcium.
Nutritional Considerations: Patients with abnormal calcium values should be informed that daily intake of calcium is important even though body stores in the bones can be called on to supplement circulating levels. Dietary calcium can be obtained from animal or plant sources. Milk and milk products, sardines, clams, oysters, salmon, rhubarb, spinach, beet greens, broccoli, kale, tofu, legumes, and fortified orange juice are high in calcium. Milk and milk products also contain vitamin D and lactose, which assist calcium absorption. Cooked vegetables yield more absorbable calcium than raw vegetables. Patients should be informed of the substances that can inhibit calcium absorption by irreversibly binding to some of the calcium, making it unavailable for absorption, such as oxalates, which naturally occur in some vegetables (e.g., beet greens, collards, leeks, okra, parsley, quinoa, spinach, Swiss chard) and are found in tea; phytic acid, found in some cereals (e.g., wheat bran, wheat germ); phosphoric acid, found in dark cola; and insoluble dietary fiber (in excessive amounts). Excessive protein intake can also negatively affect calcium absorption, especially if it is combined with foods high in phosphorus and in the presence of a reduced dietary calcium intake.
Nutritional Considerations: Educate the patient with vitamin D deficiency, as appropriate, that the main dietary sources of vitamin D are fortified dairy foods and cod liver oil. Explain to the patient that vitamin D is also synthesized by the body, in the skin, and is activated by sunlight.
Nutritional Considerations: Inform the patient with a vitamin K deficiency, as appropriate, that the main dietary sources of vitamin K are broccoli, cabbage, cauliflower, kale, spinach, leaf lettuce, watercress, parsley, and other raw green leafy vegetables, pork, liver, soybeans, mayonnaise and vegetable oils.
Reinforce information given by the patient’s HCP regarding further testing, treatment, or referral to another HCP. Answer any questions or address any concerns voiced by the patient or family. Educate the patient regarding access to nutritional counseling services. Provide contact information, if desired, for the Institute of Medicine of the National Academies (www.iom.edu).
Depending on the results of this procedure, additional testing may be performed to evaluate or monitor progression of the disease process and determine the need for a change in therapy. Evaluate test results in relation to the patient’s symptoms and other tests performed.

Related Monographs

Related tests include ALP, biopsy bone, BMD, bone scan, calcium, collagen cross-linked N-telopeptide, MRI musculoskeletal, PTH, phosphorus, radiography bone, and vitamin D.
Refer to the Musculoskeletal System table at the end of the book for related tests by body system.