Diagnosis

A number of techniques are available for measuring bone mass, each with its own advantages and disadvantages (see Table 4). Ideally, the technique should be rapid, reliable, accurate, inexpensive, and provide minimal radiation exposure. In addition, it should provide a prediction of the risk of subsequent fracture and have the ability to measure multiple sites (27).

Recommended Indications for Bone Density

Studies

• Patients being treated for osteoporosis, to monitor bone mass

• Estrogen deficient women at risk for osteoporosis

• Patients with vertebral abnormalities, hip fractures, wrist fractures, or osteopenia

Table 4. Comparison of Bone Mass Measurement Techniques

Technique

Advantages

Disadvantages

Dual energy absorptiometry Best precision for measurement of spine or

Peripheral DXA

Quantitative Computed Tomography (QCT)

Radioabsorptiometry

Single energy absorptiometry (SPA, SXA)

Ultrasound proximal femur Distinguishes between bone and soft tissue Multiple sites of measurement Low radiation exposure Moderate to low cost per test Low equipment cost Low radiation exposure Equipment portable

Distinguishes trabecular and cortical bone density

Provides measure of volumetric BMD

Low equipment cost Equipment portable

Useful for regions with low soft tissue (ie, forearm) Relatively inexpensive Equipment portable Low radiation exposure Low equipment cost Equipment portable No radiation exposure

Cannot distinguish between cortical and trabecular bone

Limited mobility of equipment Moderate equipment cost

Limited to study of wrist or heel Limited correlation to spine or hip

More difficult to perform than DXA or DPA Higher radiation exposure than DXA Meticulous performance and calibration necessary Most costly of densitometric techniques Limited mobility of equipment Small body regions evaluated

Accuracy can be severely affected by variations in fat content of marrow within the spine or femur Limited to study of phalanges Limited as a screening test Limited correlation to spine or hip Cannot measure bone mass near soft tissue (ie, vertebrae or femur) Limited correlation to spine or hip Limited as a screening test

Limited mesurement sites Limited as a screening test

• Patients receiving long-term glucocorticoid therapy

• Patients with primary hyperparathyroidism

PREVENTION OF OSTEOPOROSIS Role of Calcium

Adequate calcium is critical to achieving optimal peak bone mass and modifies the rate of bone loss associated with aging (2). Numerous studies confirm the bone sparing effect of calcium. Reid et al. found that calcium supplementation significantly slowed axial and appendicular bone loss in normal postmenopausal women who received 1000 mg of calcium supplementation daily in addition to diet. The mean rate of loss of total body bone mineral density was reduced 43% in the calcium group compared with placebo (28). Recker et al. concluded that 1200 mg calcium per day reduced the incidence of spine fractures and halted measurable bone loss in elderly women with a history of spine fractures and self-selected calcium intakes of less than 1000 mg per day (29).

cording to the Third National Health and Nutrition Examination Survey (NHANES III), the average intake of calcium by females is only 744 mg per day. For women 50 years and older, calcium intake is even lower (626-711 mg per day). The average intake for males is considerably higher at 976 mg per day, although it is lower for men 70 and older (721-808 mg) (31). Since adequate calcium intake is critical to achieving optimal peak bone mass and modifies the rate of bone loss associated with aging, calcium supplementation may be indicated in individuals who cannot meet their need by ingesting conventional foods (2).

Sources of Calcium

Dairy products are the most concentrated food sources of calcium. While green, leafy vegetables can help contribute to calcium intake, these vegetables also contain oxalic acid that can bind with calcium and interfere with absorption. The following chart lists the calcium content of some common foods. Values listed are approximate.

Recommended Calcium Intake

The NIH Consensus Development Panel on Optimal Calcium Intake defined optimal daily calcium intake as (2):

Infants birth to 6 months

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