Cummings SR, Bates D, Black DM. Clinical Use of Bone DensitometryScientific Review. JAMA. 2002;288(15):1889-1897. doi:10.1001/jama.288.15.1889
Author Affiliations: The UCSF Coordinating Center (Drs Cummings and Black), Department of Medicine (Dr Cummings), and Department of Epidemiology and Biostatistics, University of California, San Francisco (Drs Cummings and Black); and Division of General Internal Medicine and Primary Care, Brigham and Women's Hospital and Harvard Medical School, Boston, Mass (Dr Bates).
Scientific Review and Clinical Applications Section
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Context Osteoporosis causes substantial morbidity and costs $13.8
billion annually in the United States. Measurement of bone mass by densitometry
is a primary part of diagnosing osteoporosis and deciding a preventive
treatment course. Bone mineral densitometry has become more widely available
and commonly used in practice.
Objective To review evidence about the value of various clinical applications of bone densitometry.
Data Sources A MEDLINE search was performed to update previous meta-analyses of
the relationship between various measurements of bone density and risk of
vertebral and hip fracture. We used data from the prospective Study of
Osteoporotic Fractures to estimate risk of fracture from bone density and age
in postmenopausal women.
Study Selection and Data Extraction When available, meta-analyses and systematic reviews are emphasized in the review.
Data Synthesis Bone mineral density (BMD) predicts fracture and can be
used in combination with age to estimate absolute risk of fractures in
postmenopausal white women. Hip BMD predicts hip fracture more strongly than
other measurements of BMD. There are insufficient data to translate BMD results
into risk of fracture for men and nonwhite women. The benefits of treatments to
prevent fractures depend on BMD: women with osteoporosis have a greater risk of
fractures and greater benefit from treatments than women without osteoporosis.
Conclusions Guidelines based on systematic reviews and a
cost-effectiveness analysis have suggested that it is worthwhile to measure BMD
in white women older than 65 years and perhaps to use risk factors to select
younger postmenopausal women for densitometry. Other potential clinical
applications of BMD that have not yet been adequately studied include screening
men or nonwhite women, monitoring BMD in patients receiving treatment, and
using BMD to identify patients who should be evaluated for secondary causes of
Osteoporosis is important because it is common and often occult, yet
it causes substantial morbidity and costs $13.8 billion a year (1995 dollars)
in the United States alone.1 Hip fractures
account for most of the costs and deaths due to osteoporosis, but vertebral
fractures also cause substantial pain and disability, and only about a third
of these fractures are recognized clinically.2,3 Osteoporosis
is defined by low bone mass and increased fragility of bone that increases
the risk of fracture.4 Measurement of bone
mass by densitometry has become central to the diagnosis of osteoporosis and
decisions about treatment to prevent fracture.
There are no randomized trials of densitometry. We emphasize results
from prospective cohort studies, meta-analyses, and systematic reviews when
these were available. Specifically, we updated 2 meta-analyses5,6 of
the relationship between bone mineral density (BMD) and fractures by searching
MEDLINE for and including in the meta-analyses subsequent prospective cohort
studies of the relationship between various measurements of bone density and
risk of vertebral and hip fracture. Additionally, we used data from the Study
of Osteoporotic Fractures,7 a prospective community-based
study of a cohort of 9704 white women aged 65 years or older, to generate
estimates of the risk of fracture from bone density and age in postmenopausal
women. Regarding other clinical applications, we emphasize results from randomized
trials of pharmacologic treatments, prospective cohort studies, and the systematic
reviews and analyses by the National Osteoporosis Foundation8 and
the US Preventive Services Task Force.9 Many
clinical applications of densitometry have not been rigorously studied, and
we note these limitations.
Bone is composed of mineral, principally calcium hydroxyapatite, embedded
in type I collagen and specialized proteins that make up the bone matrix.
Calcium absorbs much more radiation than protein or soft tissue. The amount
of x-ray energy that is absorbed by calcium in a section reflects the bone
mineral content (BMC) (Box 1). Bone mineral content divided by the area or
volume of the bone estimates BMD. In laboratory studies, there is a high correlation
(R2 = 0.4-0.9) between BMD and the force
needed to break a bone.10- 12 Other
determinants of bone strength include size (larger bones are stronger), macroscopic
structure (long bones with greater cross-sectional areas are more resistant
to bending), microscopic structure (microscopic cracks and loss of normal
trabecular architecture weaken a bone), and the composition of bone proteins
(abnormal collagen weakens bones).
Areal Bone Density The bone mineral content
divided by the area of the image of a bone projected in 2 dimensions, which
is the type of bone density that is produced by dual- and single-energy x-ray
Bone Density or Bone Mineral Density The average
concentration of mineral in a 2- or 3-dimensional image or defined section
of bone. This term is also used to refer to the results of all types of bone
Bone Mass A nonspecific term that refers to
the amount of bone tissue as the total of protein and mineral or the amount
of mineral in the whole skeleton or in a particular segment of bone.
Bone Mineral Content The amount of mineral
measured in a defined section of bone. Total body bone mineral content refers
to the mineral content of the whole skeleton.
Broadband Ultrasound Attenuation The slope
of the line of attenuation of sound energy across a spectrum of sound frequencies.
Osteopenia A term coined by the Working Group
of the World Health Organization to refer to T scores between −1.0 and
Osteoporosis Defined by the Working Group of
the World Health Organization as a bone density T score at or below 2.5 (2.5
SDs below normal peak values for young adults). A diagnosis of osteoporosis
is also made on the basis of a vertebral fracture confirmed by radiograph.
Speed of Sound The fastest rate of transmission
of a specific frequency of sound through a defined section of bone.
Trabecular Bone Density The mineral density
of a section of bone that contains only trabecular bone.
T Score The difference in number of SDs between
the value for an individual and the mean value of a group of young (usually
25- to 45-year-old) adults of the same sex. The mean value and size of an
SD of the measurement vary between techniques and among sites of measurement.
Volumetric Bone Density The bone mineral content
of a section of bone divided by the volume of that section, which can be measured by quantitative computed tomography.
Z Score The difference in number of SDs between
the mean bone mineral density value of the individual and a group of people
of the same sex and age.
Terminology: Bone Mass, Bone Density, and BMD. Many terms are used to describe the amount and density of a bone
(Box 1). Bone mass refers to the amount of bone in the
skeleton or in one location. However, no technology produces a measurement
called bone mass. Bone mineral density is defined as the average concentration
of mineral per unit area (for single-energy x-ray absorptiometry [SXA] and
dual-energy x-ray absorptiometry [DXA]), which is also referred to as areal
BMD to emphasize that it is based on the area of the projected image of the
bone. Bone mineral density assessed in 2 dimensions is affected by the section
size of the bone: if a large and a small bone have the same mineral density,
the larger will appear to have a higher BMD. The term volumetric
bone density refers to bone mineral per defined volume of bone; volumetric
BMD does not depend on the size of a bone.
T Scores and Z Scores. Densitometry results are reported as T scores and Z scores. Both of
these rely on an SD for the measurement. An SD represents the normal variability
in a measurement in a young normal population—the distance between the
5th and 95th percentile of a group covers about 4 SDs. Standard deviations
vary from technique to technique and among various reference populations that
are used to define normal values. For hip and spine BMD, 1 SD corresponds
to about 10% to 15% of the mean value for young adults.
A Z score is the number of SDs below or above the mean BMD value for
people of the same age. A Z score of 0 means that the patient has a value
that is exactly at the mean for her age. A Z score of −2.0 means that
the patient has a BMD at that site, by that method, that is 2 SDs below the
mean BMD value of others the same age.
In contrast, a T score is the number of SDs below the mean BMD for young
(25- to 45-year-old) adults. A T score of 0 means that the patient has a BMD
value that is exactly at the mean for young adults. A T score of −2.5
means that the patient has a BMD value at that site and by that method that
is 2.5 SDs below the mean.
Because BMD declines with age, T scores are consistently lower than
Z scores after about age 40 years, and the difference increases with age.
For example, a 70-year-old patient who has a Z score of +1.0 at the hip (above
average for women of the same age) will have a T score of about −0.8
(below average compared with young women).
In general, men have higher BMD than women, and African Americans and
Latinos have higher BMD than whites.13 Asians
tend to have slightly lower BMD than whites mainly because of their smaller
size.14,15 Densitometers report
T and Z scores that are specific to the patient's sex, and some manufacturers
report values compared with those of patients of the same race. When BMD results
are interpreted in nonwhite patients, it is important to know whether the
T and Z scores are based on comparison to whites or the patient's racial group.
Prospective studies of BMD and fracture in white women provide data that permit
BMD results for white women to be translated into risks of fracture (Figure 1). However, analogous studies have
not been done for men or nonwhite women.
A number of technologies can be used to assess mineral density (Table 1), including DXA and SXA, quantitative
computed tomography (QCT), and radiographic absorptiometry. The radiation
doses for all techniques except QCT are low (less than a patient gets from
a mammogram). Quantitative ultrasound uses sound waves rather than radiation
to assess properties of bone that are related to density and bone strength.
The relationship between BMD and fracture risk is conventionally quantified
by the relative risk per SD (RR/SD), which is the increase in risk associated
with a 1-SD decrease in the BMD measurement. For example, an RR/SD of 1.6
means that fracture risk increases by 60% for each 1-SD decrease in BMD. A
larger RR/SD implies a stronger predictive value of BMD for fracture risk. Table 2 presents a summary of meta-analyses
of RR/SD for various types of BMD and fractures.
Dual-Energy X-ray Absorptiometry. Table model DXA machines can measure BMD at the hip or spine but can
also be used to measure the total amount of mineral in the whole skeleton
or forearm. Hip BMD generally refers to BMD of the femoral neck or total hip.
Bone mineral density measured at either site is a strong predictor of hip
fracture and predicts hip fracture better than BMD of other sites. Hip BMD
also predicts risk of all fractures, as do measurements at other sites (Table 2),5,6 and
is unaffected by degenerative arthritis.
Spine BMD measures vertebrae L1 through L3 or L4. Vertebral bodies are
largely made of trabecular bone that, because of its high ratio of remodeling
surface to bone volume, is more sensitive to the effects of hormones and drugs
than is cortical bone. Therefore, spine BMD tends to change more in response
to some medical conditions, such as corticosteroid excess, and to treatments
than does BMD of other sites. On the other hand, standard spine BMD, measured
in the anteroposterior direction, includes mineral in the posterior elements
and facet joints as well as the abdominal aorta, none of which contribute
to the strength of the vertebral body. Consequently, spine BMD is increased
by degenerative arthritis and, for this reason, tends to increase after about
age 65 years rather than decrease, as seen in other BMD measurements.19
Peripheral Densitometry. Smaller devices use DXA or SXA to measure bone density in the forearm
or heel. The distal radius is often used because it contains trabecular and
cortical bone. A peripheral test generally costs much less than DXA of the
hip and spine (Table 1). These
tests are predictive of fractures20 but less
predictive than BMD at the hip for hip fractures and somewhat less accurate
at predicting vertebral fractures than hip or spine BMD (Table 2). The proportion of patients with T scores less than −2.5
varies considerably from one type of device to another.20,21
Quantitative Computed Tomography. Quantitative computed tomography of the spine is available on standard
computed tomography devices, and a smaller device, known as peripheral QCT,
performs QCT at the distal forearm. Quantitative computed tomography is unique
because it assesses 3-dimensional bone density and permits isolated measurement
of trabecular bone density.22 The value of
QCT measurements for prediction of fractures, and therefore for making clinical
decisions, has not been well studied.
Measurements Based on Radiographs. Radiographic absorptiometry compares the density of proximal phalanges
to that of a wedge of aluminum that has known densities and is placed on the
film alongside the hand.23 Other hand radiograph-based
techniques allow estimation of bone density from cortical thickness.24 Characteristics and costs of methods based on hand
films are similar to those of peripheral densitometry.
The integrity of bundles of trabeculae that run through the proximal
femur can be qualitatively rated by the Singh index.25 The
cortical width of the femoral neck is another index of osteoporosis. Prospective
studies have shown that these measurements also predict hip fracture risk.26,27
Quantitative Ultrasound. The transmission of sound through bone reflects its density and structure
and can be assessed quantitatively by the speed of sound, the pattern of absorption
of different wavelengths of sound, called broadband ultrasound attenuation,
or calculations derived from these parameters.28- 30 Quantitative
ultrasound of the heel resembles other peripheral measurements in terms of
ability to predict fractures (Table 2),
and the combination of calcaneal broadband ultrasound attenuation and femoral
neck BMD predicts hip fracture risk somewhat better than either measurement
Prediction of Fracture Risk. Prospective studies have established that fracture risk increases as
BMD decreases, and there is no fracture threshold below which fracture risk
abruptly increases (Figure 1).7,32,33 Therefore, BMD is
best thought of as a continuous risk factor: the lower the BMD, the higher
the risk of fracture.
A woman's risk of fracture can be estimated from her age and BMD. Table 3 provides estimates of lifetime
risk of hip fracture for white women at various ages and levels of femoral
neck bone density. Figure 1 also
provides estimates of risk of nonspine, vertebral, and hip fracture at various
ages and levels of hip BMD. These estimates would be somewhat different for
hip BMD measured with another device (other than a Hologic brand) and very
different for BMD at other sites, such as the spine or forearm.
One might expect that a BMD measurement at a specific site would be
most predictive of fractures at that site, as is true for hip BMD predicting
hip fracture (Table 2). However,
hip and spine BMD have similar accuracy for predicting vertebral fractures,
and all sites and types of measurement seem to have similar accuracy in predicting
the general risk of all fractures.5,35
Value of Risk Factors for Assessing Risk. Several risk factors, especially age, sex, weight, and race, are correlated
with BMD. However, it is impossible to predict BMD from combinations of risk
factors with clinically useful accuracy.36- 38 Guidelines
have used the presence of risk factors to recommend measurement of BMD
(Box 2). Several short instruments have been developed to identify women who have
a low probability of having osteoporosis on measurement of BMD. These instruments and scoring systems have high sensitivity (identifying 95%-99% of women who have osteoporosis defined as a T score ≤−2.5 at the hip) but poor specificity (only 10%-25% of postmenopausal women without osteoporosis would avoid testing).
National Osteoporosis Foundation
The decision to test for bone mineral density (BMD) should be based
on an individual's risk profile, and testing is never indicated unless the
results are likely to influence a treatment decision.
BMD Testing Recommendations1. Postmenopausal women 65 years or older, regardless of additional
risk factors. This recommendation includes women 65 years or older who have
been taking osteoporosis therapy and have not had a BMD test.
2. Postmenopausal women younger than 65 years and with 1 or more additional risk factors for osteoporosis.*
3. Postmenopausal women who have had a fracture of any type as an adult
after age 45 years.
US Preventive Services Task Force (USPSTF)
Summary of Recommendations. The USPSTF "recommends
that women 65 years of age and older be screened routinely for osteoporosis.
The USPSTF recommends that routine screening begin at 60 years of age for
women at increased risk for osteoporotic fractures."9
"The USPSTF makes no recommendation for or against routine osteoporosis
screening in postmenopausal women who are younger than 60 years of age or
in women 60 to 64 years of age who are not at increased risk for osteoporotic
*Risk factors include parental history of hip fracture, current cigarette
smoking, a body weight less than 57.2 kg, use of (or plans to use) oral corticosteroids
longer than 3 months, or serious long-term conditions thought to increase
fracture risk, such as hyperthyroidism or malabsorption.
Some risk factors for fracture are independent of BMD, that is, they
improve the prediction of fracture even when BMD is known. For example, a
woman who has a vertebral fracture has a 4-fold increase in risk of another
vertebral fracture regardless (or independent) of her BMD.39,40 Risk
factors that predict hip fracture independently of BMD include age, history
of fracture,41,42 maternal history
of hip fracture, conditions that increase the risk of falling,43,44 increased
levels of markers of bone resorption,45 and
very low serum levels of estradiol.46 In prospective
studies, Black et al47 found that risk factors
obtainable by history can also be used to estimate risk of hip fracture, and
measurement of BMD improves the prediction somewhat. Assessing risk factors
might help in making decisions about treatment when densitometry is unavailable
or when the best course is unclear from a patient's bone density.
Diagnosing Osteoporosis and "Osteopenia." Since the relationship between decreasing bone density and increasing
risk of fractures is a continuous one, there is no threshold or cutoff value
to distinguish low- and high-risk people. However, medical practice and reimbursement
sometimes require a diagnosis of osteoporosis. The World Health Organization
defined osteoporosis as a T score of −2.5.48 This
cutoff has no inherent biological meaning; it was created to allow comparisons
of the prevalence of osteoporosis in different countries and was not intended
to be used to make treatment decisions.
The diagnosis of osteoporosis according to BMD can be confusing because,
if 2 or more sites are measured, patients will sometimes have a T score of
−2.5 or less and so-called osteoporosis at one site and above that level
at other sites.21 Some experts and guidelines
consider a T score at or below −2.5 at the femoral neck or total hip
to be the gold standard for the diagnosis of osteoporosis. Others prefer to
diagnose osteoporosis if the T score at either the hip or spine is at or below
−2.5; the latter approach designates more women as osteoporotic who
will, on average, have a somewhat lower risk of fracture.49
Osteopenia was defined by the WHO conference as a bone density T score
between −1.0 and −2.5.48 The upper
cutoff, a T score of −1.0, was also chosen arbitrarily to indicate women
whose bone density was below normal for young adults. More than half of postmenopausal
women could be called osteopenic at at least 1 site of measurement.13,50 The term has limited value because
it encompasses a broad range of women, including some with a relatively high
risk for their age and others whose risk is lower than average for their age
(Figure 1). It is more useful and
less alarming to patients to avoid this term and instead to focus on their
risk of fractures.
Most of a person's BMD, even after age 65 years, is genetically determined.
Some uncommon conditions, including Cushing disease, malabsorption, hyperparathyroidism,
and hyperthyroidism, can decrease bone density. Finding and treating these
conditions might decrease a patient's risk of fractures. Unfortunately, the
chance of finding a secondary cause in patients with low BMD, especially in
primary care settings, is unknown, and the value of testing for secondary
causes in women with low BMD has not been adequately studied. It is believed
that the chance of finding a secondary cause increases as BMD decreases at
a specific age.51 If so, then a low Z score
(<−2.0 or −3.0) might be a more useful guide than the T score
in deciding whether to look for secondary causes of osteoporosis. Some physicians
also screen for secondary causes in women with osteoporosis defined by a low
T score, although the best approach is uncertain.
Bone mineral density can help determine whether a fracture is due to
osteoporosis. For example, BMD may be valuable if a patient has a vertebral
fracture in a location that would be unusual for osteoporosis, such as T4.52 Although there is no evidence about this point, it
is reasonable to believe that the higher the BMD, the greater the chance that
another process, such as cancer or trauma, caused the fracture.
Women with vertebral fractures have a high risk of fractures, and several
approved treatments decrease their risk of future vertebral fracture. Among
women without a vertebral fracture, the potential benefit of treatment depends
on the patient's bone density: the lower the BMD, the greater the likelihood
that she will benefit from treatment to prevent fractures.
A systematic review and cost-effectiveness analysis used data available
up to 1996 and estimated that it was worthwhile to recommend drug treatments
that reduce risk of hip fracture to women with low femoral neck BMD (T scores
below −3.0 to −1.5, depending on age, risk factors, and type of
treatment).8 Several drugs have been approved
by the Food and Drug Administration for treatment of osteoporosis (alendronate,
risedronate, raloxifene, and calcitonin) because they reduce the risk of fractures
among women who have vertebral fractures or osteoporosis defined as a T score
of −2.5 or less at the femoral neck or spine.53- 58 The
value of treating women without vertebral fractures who have higher levels
of BMD is less certain. In the Fracture Intervention Trial,54 4
years of alendronate treatment significantly reduced the risk of hip and other
nonspine fractures, including hip fractures among women whose hip BMD T score
was less than −2.5, but not in women with a higher starting BMD. Women
with T scores above −2.5 had a reduction in risk of vertebral fractures,
although the absolute reduction in risk was much greater in women with osteoporosis
than in those with T scores above −2.5. Risedronate reduced the risk
of hip fracture among women who were younger than 80 years and whose femoral
neck BMD T score was at least below −3.0, but it did not significantly
reduce the risk of hip fractures among women who were older than 80 years
and were included because they had risk factors for hip fracture regardless
of BMD. These studies suggest that hip BMD may be a valuable indicator of
who will benefit most from reduction in risk of nonspine and hip fractures
after several years of treatment with bisphosphonates. In contrast, no published
study has evaluated the ability of spine and peripheral measurements of BMD
to identify women who benefit most from treatments to reduce the risk of fractures.
Using a systematic review and cost-effectiveness analysis,8 the
National Osteoporosis Foundation recommended measuring BMD, preferably of
the hip, for all white women 65 years or older who are not receiving drugs
that are approved for treating osteoporosis.59 Additionally,
these guidelines suggested measuring BMD for younger postmenopausal women
who were aged 50 to 65 years and had another strong and well-established risk
factor for osteoporosis.
The United States Preventive Services Task Force recommended routine
screening for osteoporosis beginning at age 65 years in all women and at age
60 years in women with risk factors indicating an increased risk of osteoporotic
fractures. It made no recommendation about screening for women younger than
60 years (Box 2).
Men and nonwhite women have a lower overall fracture rate than white
women, but there are insufficient data on which to base recommendations about
BMD in men and nonwhite women. Alendronate reduces fracture risk in men,60 and it is reasonable to believe that treatment would
be worthwhile for men and nonwhite women who have a decreased BMD and risk
of fracture that is similar to that of white women with osteoporosis. However,
there is controversy about what levels of BMD should be considered osteoporotic
and what values should trigger a recommendation for drug treatment in men
and nonwhite women.
Women Who Are Considering Stopping Estrogen Therapy. Estrogen therapy improves bone density61 and
reduces the risk of fracture62 but does not
fully prevent women from developing osteoporosis. One large study found that
4% of women who were older than 65 years and had taken estrogen continuously
since menopause and 11% who started after menopause had hip BMD T scores below
−2.5.63 Women who stop taking estrogen
generally lose bone and appear to lose any protection against fractures within
a few years.64,65 Therefore, it
is reasonable to recommend densitometry to women 65 years or older and younger
women who have risk factors for fracture and wish to stop long-term estrogen
therapy. If they have osteoporosis, it is reasonable to recommend treatment
with an agent that has been shown by randomized trials to reduce fracture
Bone mineral density is often measured every 1 or 2 years during treatment
to determine whether a patient is responding to treatment. However, interpreting
these results is tricky; the meaning of changes in BMD during treatment is
uncertain because responding is not the same as gaining BMD. A patient who
loses BMD, eg, 3%, during treatment may be responding because she could have
lost more (eg, 5% to 6%) without treatment. Furthermore, most patients who
seem to lose BMD during the first period of treatment regain much of that
BMD during the next period, even if treatment is unaltered.66 In
addition, women who seem to lose BMD while taking alendronate may have a reduction
in risk of vertebral fracture similar to that of women who gain BMD.67 Thus, treatments should not be changed because the
patient appears to lose BMD during the first period of monitoring. The value
of changing or adding treatments in women who persistently lose BMD has not
It is also important to recognize that small changes in BMD may be due
to the random variability in the test. The least significant change in BMD
is the percentage of change that is unlikely (usually <5% chance) to be
due to the precision error of the test.68 Least
significant change is calculated as 2.8 times the precision error of the test
on a specific machine and site of measurement. Femoral neck BMD has about
a 2% precision error in expert centers; therefore, changes of less than about
5.6% can often be due to precision error.
The best approach to monitoring BMD in patients who are not receiving
pharmacological treatment is uncertain. Many patients have BMD levels too
high to warrant treatment at screening, but their BMD may later decline to
a level at which pharmacological treatment is indicated. It would be reasonable
to repeat BMD when the result probably would change treatment. After about
60 years of age, women generally lose less than 1% of hip BMD annually, and
their rate of change at the spine is on average even slower,69 so
that it would usually take more than 10 years to decline a full point in T
score (for example, from −1.5 to −2.5). Bone mineral density may
decline somewhat more rapidly in women who are within 5 years of menopause.
The timing of the repeat measurement depends on the current BMD: the closer
the current value is to a threshold where treatment would be started, the
sooner the BMD measurement should be repeated.
Which BMD Site Should Be Measured? Because BMD at the hip is the best predictor of hip fracture, hip BMD
may be particularly useful in women older than 65 years, since risk of hip
fracture rises rapidly after age 65. Reports of hip DXA include several subregions
of the hip, but these results are highly correlated and have similar predictive
value for fractures.7,70 If only
1 site is measured, then BMD of the hip (femoral neck, total hip, or both)
may be preferable because of its predictive value for hip fractures, and it
has been better standardized for diagnosis of osteoporosis.13 Spine
and hip BMD have similar value for predicting spine fractures (Table 2). As noted earlier, spine BMD tends to be artificially increased
in women 65 years or older, which may limit its predictive and diagnostic
value in that age group. Spine BMD is more sensitive to the effects of corticosteroids
and may be the best choice for assessing and monitoring corticosteroid-treated
Peripheral vs Central Measurements.
As noted earlier, peripheral measurements (such as the forearm) are
less expensive, more widely available in some areas, and predictive of overall
fracture risk, but peripheral measurements do not predict hip fractures as
well as hip BMD. Treatments tend to produce smaller changes in peripheral
measurements than in spine or hip BMD.53,72 Peripheral
measurements might be used as initial screening tests for referring patients
who have low BMD for DXA of the hip or spine.
How Many Measurements Should Be Made? Dual-energy x-ray absorptiometry examinations usually include hip and
spine BMD for the same price as 1 measurement. The T and Z scores from these
sites often differ, which can confuse physicians and patients. Because of
the stronger relationship of hip BMD to hip fracture and weaker influence
of degenerative arthritis after age 65 years, it is reasonable to give more
weight to the results of hip BMD. However, some practitioners base decision
making on the lowest value. There are insufficient data to determine which
approach is best. If hip or spine BMD has been measured, there is generally
no reason to measure a peripheral site.
Prospective studies are under way to better describe the relationship
between BMD and risk of fractures in men, and groups are developing models
that will allow physicians to combine BMD results and risk factors into estimates
of a patient's absolute risk of fractures.73
There is a growing appreciation that current methods of measuring average
BMD in a 2-dimensional projection of bone may miss important information about
bone structure; connectivity of trabecular bone, the width of cortical bone,
or the degree of aggressive remodeling along the endocortical surface might
all play an important role in determining bone strength. Research is under
way to develop and test the clinical value of new methods such as magnetic
resonance imaging or high-resolution QCT for assessing risk of fractures and
response to treatment.
Current methods of bone densitometry are powerful tools for assessing
the risk of fracture and identifying patients who will benefit most from the
treatments that have been shown to reduce fracture risk in patients with osteoporosis.
Selective use of densitometry is a valuable part of primary care of postmenopausal