Context Identification of women with low bone mineral density (BMD) is an important
strategy in reducing the incidence of osteoporotic fractures. However, screening
all women is not recommended.
Objectives To assess the diagnostic properties of 4 decision rules—Simple
Calculated Osteoporosis Risk Estimation (SCORE), Osteoporosis Risk Assessment
Instrument (ORAI), Age, Body Size, No Estrogen (ABONE), and body weight less
than 70 kg (weight criterion)—for selecting women for dual-energy x-ray
absorptiometry (DXA) testing and to compare results with recommendations made
in the National Osteoporosis Foundation (NOF) practice guidelines.
Design and Setting Analysis of data from the Canadian Multicentre Osteoporosis Study, a
population-based community sample, collected from 9 study centers across Canada
between February 1996 and September 1997.
Participants Postmenopausal women aged 45 years or older (N = 2365) without bone
disease who had DXA data for the femoral neck, data to apply selection criteria,
and who were not currently taking estrogens or who had been taking hormone
replacement therapy for 5 or more years.
Main Outcome Measures Sensitivity, specificity, and area under the receiver operating characteristic
(AUROC) curve of each of the 4 decision rules and the NOF guidelines for identifying
women with a BMD T score of less than −1.0 SD, less than −2.0
SD, and no more than −2.5 SD at the femoral neck, and percentages of
women recommended for testing, stratified by BMD level and age.
Results The percent of women with a BMD T score less than −1, less than −2,
and no more than −2.5 were 68.3%, 25.4%, and 10.0%, respectively. The
AUROC curves were greatest using SCORE and ORAI. The sensitivity for identifying
women with a BMD T score of less than −2.0 was 93.7% (95% confidence
interval [CI], 91.8%-95.6%) using the NOF guidelines and was 97.5% (95% CI,
96.3%-98.8%), 94.2% (95% CI, 92.3%-96.1%), 79.1% (95% CI, 75.9%-82.3%), and
79.6% (95% CI, 76.4%-82.8%), respectively, using the SCORE, ORAI, ABONE, and
weight criterion. However, the NOF guidelines also resulted in 74.4% (95%
CI, 71.3%-77.6%) of women with a normal BMD (T score of −1.0 or higher)
being tested compared with 69.2% (95% CI, 65.9%-72.5%), 56.3% (95% CI, 52.7%-59.8%),
35.8% (95% CI, 32.4%-39.2%), and 38.1% (95% CI, 34.6%-41.6%), respectively,
using the 4 decision rules. Assessments suggest that ABONE and weight criterion
are not useful case-finding approaches.
Conclusion The SCORE and ORAI decision rules are better than the NOF guidelines
at targeting BMD testing in high-risk patients. The acceptability of these
rules in clinical practice merits further investigation given their potential
effect on the use of densitometry services.
The identification of women at risk for osteoporotic fractures by measurement
of low bone mineral density (BMD) is an important strategy to reduce the burden
of fracture-related morbidity associated with this disease.1,2
Dual-energy x-ray absorptiometry (DXA) is accepted as the most accurate clinical
method for identifying those with low BMD.2,3
Suggestions concerning who should be tested are quite broad. The National
Osteoporosis Foundation (NOF) 1998 practice guidelines (revised in 1999)4 recommend BMD testing in women considering treatment
who are aged 65 years or older, and in younger postmenopausal women considering
treatment who have 1 or more risk factors for osteoporotic fracture other
than menopause. The recommendation to select perimenopausal women on the basis
of "other risk factors" is echoed in a number of other guidelines.2,5-9
However, given that many postmenopausal women have at least 1 of these factors,10 the question may not be whom to test, but rather
whom not to test.
Clinical decision rules are evidence-based tools that can help reduce
uncertainty in medical practice by implementing clear criteria for the use
of major clinical findings.11,12
Several decision rules based on clinical criteria have been developed to guide
decisions for BMD referrals.13-16
They range from the very simple, being based on weight alone,13
to more complex selection schemes requiring the assessment of many risk factors.14 The purpose of this study was to assess the diagnostic
properties of the NOF recommendations and 4 decision rules.4,13-16
The Canadian Multicentre Osteoporosis Study (CaMos) is a population-based
5-year cohort study evaluating the relationship between risk factors for osteoporosis,
measures of BMD, and osteoporotic fracture.17
In brief, an age-, sex-, and region-stratified random sample of the Canadian
population was selected using a telephone-based sampling frame. This included
noninstitutionalized residents aged 25 years or older within 50 km of 9 study
centers across Canada. CaMos participants were fluent in English or French,
or in the case of Toronto and Vancouver, English, French, or Chinese. Baseline
data collection began February 1996, and ended September 1997. Eligible subjects
were invited to meet with a trained interviewer to complete a standardized
questionnaire about risk factors for osteoporosis and to visit the center
for DXA testing. The present study included data from 6 sites: Calgary, Halifax,
Québec City, Saskatoon, St John's, and Vancouver. Given that the Osteoporosis
Risk Assessment Instrument (ORAI) was developed using CaMos Ontario data (Hamilton,
Kingston, and Toronto),15 these sites were
excluded from the current analyses. Menopausal women aged 45 years or older
with DXA data at the femoral neck were eligible for this study. Participants
with physician-diagnosed bone disease, taking bone sparing medication other
than ovarian hormones, or missing data for any of the risk factors required
by the decision rules or NOF guidelines were excluded.
The NOF guidelines4 and the decision
rules each provide guidance to clinicians in making referrals for BMD testing.
The recommendations are made to help identify the average woman at risk for
primary osteoporosis. Identification of women at high risk for secondary osteoporosis
would be independent of respective recommendations for testing. Therefore,
women at high risk for secondary osteoporosis were excluded from this study.
The NOF guidelines recommend BMD testing only among women considering treatment,
ie, when there is a decision to be made. For the purposes of this study it
was assumed that all women would consider treatment depending on DXA results.
Although women currently taking hormone replacement therapy (HRT) would not
be eligible for testing (no decision to be made regarding treatment), the
NOF physician's guide recommends testing in those taking HRT for prolonged
periods. As a result, whereas women taking HRT for less than 5 years were
excluded, those taking HRT for 5 years or more were included in the study.
Inclusion of Decision Rules for Referring Women for Bone Densitometry
We conducted a MEDLINE search to identify articles published in English
providing decision rules based on simple criteria to identify menopausal community-dwelling
women for BMD testing. Decision aids based on regression models18
or involving detailed questionnaires19 were
excluded from this analysis. Our search identified 4 decision rules for BMD
testing.13-16
Application of NOF Guidelines and Decision Rules
Table 1 summarizes the criteria
that clinicians are recommended to use in deciding which women should undergo
bone densitometry under the NOF guidelines and the 4 decision rules. Each
strategy was applied to the cohort using individual responses to the CaMos
questionnaire. Among women 65 years or younger, selection criteria were limited
to the 4 major risk factors highlighted in the NOF physician's guide, ie,
weight less than 57.6 kg, personal history of fracture as an adult, history
of fracture in a first-degree relative, and current smoker. These 4 criteria
were chosen by the NOF20 because they are key
determinants of hip fracture risk among white women.21
The NOF guideline specifies family history to include maternal or paternal
wrist, hip, or spine fracture after the age of 50 years. These specific data
were not collected by CaMos. Therefore, any parental minimal trauma fracture
was used as a proxy. The CaMos questionnaire grouped fractures of the forearm
and wrist. Minimal trauma fractures of the forearm/wrist were included as
a history of wrist fracture in Simple Calculated Osteoporosis Risk Estimation
(SCORE) derivation. Finally, weight was recorded in kilograms by CaMos.
Bone mineral density was measured using the following DXA machines:
Hologic QDR 4500 (in Calgary), Hologic QDR 2000 (in Halifax and Québec),
Hologic QDR 1000 (in Saskatoon and Vancouver) (Hologic Inc, Waltham, Mass),
and Lunar DPX (in St John's), (Lunar Corporation, Madison, Wis). T scores
were calculated from cross-calibrated Hologic BMD equivalents22
using Canadian young adult normal values at the femoral neck.23
Although a recent update from the International Osteoporosis Foundation3 suggests that the Third National Health and Nutrition
Examination Survey (NHANES III) reference data be used to derive T scores,
there is increasing evidence supporting local reference standards.24 As well, the Canadian young adult normal reference
at the femoral neck (mean [SD], 0.857 [0.125] g/cm2)23
is similar to that reported by NHANES III for non-Hispanic white Americans
(mean [SD], 0.858 [0.120] g/cm2).25
Low BMD at either the hip or lumbar spine is clinically relevant for
deciding about prophylactic treatment to prevent osteoporosis and fragility
fractures.5 However, given that the NOF guidelines4 were derived from assessments at the hip and the increasing
questions regarding the application of the World Health Organization criteria
to sites other than the hip,3 BMD outcomes
in this study were assessed as being present at the femoral neck.
Osteoporosis treatment guidelines4-7
suggest pharmacological interventions among those with osteoporosis (T score ≤ −
2.5 SDs) and no intervention among women with normal BMD (ie, T score ≥−1.0).
While most guidelines2,5-7
suggest that treatment be considered for those with osteopenia (T score of −1.0
to −2.5), the NOF guidelines provide more specific recommendations;
suggesting treatment to reduce fracture risk among menopausal women with a
BMD T score below −1.5 if other risk factors are present, or below −2.0
in the absence of risk factors.4 For the purposes
of this analysis, a T score of less than −2.0 was taken as the suggested
threshold to initiate pharmacological therapy to reduce fracture incidence
in menopausal women, hereafter referred to as the treatment
threshold.
Demographic and other characteristics of the study population were tabulated
as means and SDs, or proportions as applicable. The area under the receiver
operating characteristic (AUROC) curve was used as a measure of the overall
ability of each strategy to discriminate between women with varying degrees
of low BMD. Three BMD outcomes were examined for each strategy: a BMD T score
of less than −1.0 (complement of normal BMD4-7),
less than −2.0 (below treatment threshold), and no more than −2.5
(osteoporosis4-7).
The AUROC curves were calculated and compared with applying methods for correlated
AUROC curves.26 The AUROC curves for identifying
osteoporosis were plotted.
The decision rules are scoring systems amenable to AUROC curve analysis.
Although the NOF recommendations are not presented as a scoring system, the
guide states that the more risk factors a women has, the greater the risk
for fracture.4 The status report20
summarizing evidence-based recommendations suggested that physicians use a
counting method of risk factors among menopausal women aged 65 years or younger,
giving 1 point for history of fracture, weight, and smoking. We thus derived
"NOF points" by giving 1 point to each factor.
The number of points recommended by the developers of respective decision
rules was used to select women for testing, ie, SCORE points of 6 or more,
ORAI points of 9 or more, Age, Body Size, No Estrogen (ABONE) points of 2
or more, body weight of less than 70 kg (weight criterion), and NOF points
of 1 or more. Given the discrepancy between the text and scoring in the ABONE
article, we contacted the author who confirmed that patients with an ABONE
score of 2 or more are recommended for testing (L. Weinstein, written communication,
February 2001).16 Sensitivity, specificity,
and corresponding 95% confidence intervals (CIs) were calculated at the recommended
cut-point for each method. Finally, given that 2 of the selection methods
(NOF and ORAI) recommend all women aged 65 years or older for testing, the
proportion of women selected by each tool was stratified by age as 45 to 64
years old and 65 years or older, and presented by level of BMD as: normal
BMD (T score ≥−1 SD), mild osteopenia (T score −1.0 to no less
than −2.0), moderate osteopenia (T score −2.0 to −2.5),
and osteoporosis (T score ≤−2.5).
A total of 3288 menopausal women aged at least 45 years had DXA data
at the femoral neck. Among these, a total of 402 were excluded with either
a diagnosis of osteoporosis (382) or taking bone sparing medications such
as calcitonin or bisphosphonates (20). A further 158 were excluded with potential
causes for secondary osteoporosis. In addition, 69 were missing data to calculate
decision rules, and 294 currently using HRT for less than 5 years were excluded,
leaving a total sample size of 2365 women.
The mean age and weight of the study cohort was 66.4 (SD, 8.8) years
and 69.0 (13.3) kg, respectively. Table
2 provides a summary of demographics, osteoporosis risk factors,
and the distribution of BMD in the study cohort. The population under investigation
was largely composed of white women (96.6%). Among those younger than 65 years
(n = 978), 43.5% had normal BMD, 52.1% had osteopenia (26.1% of whom fell
below the treatment threshold), and 4.7% had osteoporosis.
The sensitivity and specificity at the developers' recommended cut-point
and the AUROC curve for each approach to select women with any clinically
significant decrease in BMD (T score <−1.0), below the treatment
threshold (T score <−2.0), and with osteoporosis (T score ≤−2.5)
are presented in Table 3. The
AUROC curves for identifying women with osteoporosis are plotted in Figure 1. The SCORE and the ORAI had the
best discriminatory performance at all BMD thresholds evaluated. When restricted
to osteoporosis, SCORE, ORAI, and weight criterion were equivalent, with an
AUROC curve of 0.80, 0.79, and 0.79, respectively.
The NOF, SCORE, and ORAI selection criteria resulted in more than 94%
of women below the treatment threshold and more than 96% of women with osteoporosis
for initial testing, with SCORE being the most sensitive. However, NOF and
SCORE would also recommend 74.4% (95% CI, 71.3%-77.6%) and 69.2% (95% CI,
65.9%-72.5%) of women with normal BMD for testing, compared with 56.3% (95%
CI, 52.7%-59.8%) with the ORAI. The other decision rules would miss from 13%
to 17% of women with osteoporosis but result in less than 40% of women with
normal BMD recommended for testing: 35.8% (95% CI, 32.4%-39.2%) with ABONE
and 38.2% (95% CI, 34.6%-41.6%) using the weight criterion.
The overall proportion of women selected by each method ranged from
55% to 84% (Table 4). The NOF
and SCORE would each result in 84% of women aged 45 years or older being recommended
to undergo DXA testing. The corresponding figures for the other decision rules
were 75% of women for ORAI and 55% and 56% for ABONE and weight criterion,
respectively. When looking at results by age, the SCORE selected 95% of women
aged 65 years or older, coming close to the recommendations made by the NOF
and ORAI that include women aged 65 years or older as part of their selection
criteria. However, the SCORE also selected a higher proportion of younger
women (69%), particularly in comparison to the ORAI (39%) and the ABONE (22%).
This translates into 55% of women aged 45 to 64 years with normal BMD being
selected by SCORE (comparable to the NOF), compared with 23% and 12% using
the ORAI and ABONE, respectively. The weight criterion selected 53% of younger
vs 59% of older women, the closest proportion by age compared with any other
method. However, the weight criterion only captured 83% of younger women and
79% of older women below the treatment threshold. Although ABONE selected
88% of older women below the treatment threshold, more than half of younger
women with moderate osteopenia and osteoporosis were missed.
In recent years, the availability of new pharmacological treatments
for osteoporosis27 have put new pressures on
primary care physicians to screen patients at risk for fragility fracture
with BMD testing. The clinical challenge is to identify those at greatest
risk for fracture,1 while limiting unnecessary
testing in those with normal BMD who have a low risk for fracture.1,6 Current guidelines2,5-9
providing lists of indications for BMD testing may be difficult to translate
into a clinical case-finding strategy for practice.12,28
Decision rules using a more limited, but specific set of clinical factors
provide an alternative approach to guide decisions for BMD testing.
Two of the decision rules (SCORE and ORAI) as well as the NOF guidelines
selected 94% or more women below the treatment threshold and more than 96%
of women with osteoporosis. However, the specificity of the ORAI was significantly
better, selecting 56% of women with normal BMD compared with 69% and 74% with
the SCORE and NOF, respectively. Although the ABONE and weight criterion would
result in even fewer tests (<40%) among women with normal BMD, 20% of women
below the treatment threshold would not be selected for DXA testing.
Overall, the NOF guidelines and SCORE each selected 84% of the study
population. The ORAI selected significantly fewer women (75%), yet recommended
just as many women aged 45 to 64 years with moderate osteopenia (67%), and
more women with osteoporosis (87% vs 80%) compared with the NOF guidelines.
Therefore, the ORAI, similar to the NOF in selecting all women aged 65 years
or older, is clearly superior to the NOF guidelines, providing more specific
recommendations to limit unnecessary testing among women younger than 65 years.
Similarly, given that the tools have comparable performance, the simplicity
of the ORAI vs the SCORE suggests that it might be more readily adopted in
clinical practice,12 and thus may have a better
impact on identifying women for initial BMD testing vs the SCORE. An impact
assessment11 of the 2 rules is warranted to
assess the effectiveness of these decision rules applied in practice. Future
research should evaluate the SCORE and ORAI critically from the perspective
of both physicians and health planners/policy advisors. Clinicians may not
favor using a rule that limits testing in women who may be appropriately selected
for treatment on the basis of BMD results, preferring instead to use clinical
judgment, or to opt for universal screening. However, a policy for screening
all menopausal women has been widely rejected, and it may be difficult for
clinicians to assign appropriate weight to multiple risk factors in each patient
individually. Decision rules may therefore be more productive in terms of
useful decision making.11 Decision rules are
not meant to replace diagnostic tests, but rather complement them by helping
to identify higher risk populations that are more likely to benefit from testing.11 Clinical decisions for treatment should be based
on actual DXA bone density values and the patient risk profile, rather than
relying on the decision rule results.
Targeting high-risk populations is important for achieving cost-effective
interventions.29 Selection of women aged 65
years or older makes intuitive sense, because women at this age are entering
the highest period of risk for hip fractures,30
and supports the view that screening should likely be aimed at women aged
65 years or older.31 Both the ORAI and the
NOF practice guidelines suggest BMD testing in all women aged at least 65
years who are considering treatment, regardless of risk profile. At the recommended
cut-point of 6, the SCORE also selected 95% of women in this age group. However,
other researchers have begun to explore specific selection criteria aside
from age among older groups. Currently, this is limited to regression models32 that would not be easy to implement in a clinical
setting.12 Others argue that there is an upper
age limit beyond which DXA testing is not necessary (>80 years,33
>70 years4), supporting treatment among these
oldest age groups in the presence of multiple risk factors without DXA. Further
research is warranted, however, to identify the effectiveness of treatment
without BMD results. A recent randomized controlled clinical trial identified
the importance of BMD testing in making decisions for drug therapy, finding
that risedronate reduced fracture incidence among elderly women with low BMD,
but no protection was observed among those selected based on clinical factors
other than BMD status.34
Data in this study provide information based on DXA results at one point
in time. The purpose of initial DXA testing is to identify those who would
benefit from treatment or prophylaxis to reduce the risk of fragility fracture
based on low BMD. As such, the ultimate outcome of interest is fracture, and
future studies should evaluate the proportion of missed cases that eventually
fracture. Such longitudinal evaluation may also provide information regarding
the repeated use of decision rules to select women for initial DXA testing.
Furthermore, in addition to BMD results, the best predictor of fracture is
prevalent fracture. The NOF recommendations include prevalent fracture as
an indication for BMD testing. Although the SCORE includes a variant of this
(gives points for previous fracture), it would not select all of these patients.
Likewise, minimal trauma fractures were associated with low BMD in development
of the ORAI, but fracture history was excluded from the decision rule to simplify
the instrument.15 Similar to the separate identification
of women at high risk for secondary osteoporosis, it is important in practice
to suggest absolute BMD testing among those with prevalent fragility fracture
if they are considering treatment. The simple screening and treatment of individuals
with fragility fracture are often neglected in practice.35-37
Given that CaMos oversampled older age groups, our study sample had
proportionately more women older than 65 years as compared to the actual distribution
of menopausal women in Canada. This may have affected the overall specificity
of each selection method and overestimated the total proportion selected by
each tool. Given that we did not have specific data regarding age or site
of fractures in parents, by including any parental minimal trauma fracture,
we may have overselected women for testing based on NOF. In addition, rheumatoid
arthritis is a known cause of secondary osteoporosis.4
Given the inclusion of rheumatoid arthritis in SCORE derivation, we included
subjects with this condition. Inclusion of women with rheumatoid arthritis
may have increased the sensitivity of the SCORE, but decreased the sensitivity
of the other selection methods that target women at risk for primary osteoporosis.
Finally, among initial contacts providing basic demographic data, the response
rate for women aged 45 years or older among the 6 CaMos sites included in
this study was 62.1%. Proportions agreeing to participate decreased with increasing
age, from 75.7% among those aged 45 to 54 years to 35.7% among those older
than 84 years. This may indicate a healthy cohort effect, where healthier
women participated in the study, and thus an underrepresentation of frail
and sick individuals at older ages. Alternatively, given the nature of the
study, which evaluates risk factors for osteoporosis, perhaps a different
self-selection bias occurred, where those at higher risk or with a family
history were more likely to participate in the study. Further evaluations
in other populations are important to access the generalizability of these
findings.
DXA testing is important for evaluating the severity of bone loss and
making treatment decisions. The ABONE and weight criterion decision rules
miss 13% to 17% of women with osteoporosis and are thus not useful case-finding
approaches for DXA testing. The SCORE and the ORAI, however, are better than
the NOF guidelines, targeting testing on women at high-risk for low BMD. The
acceptability of these rules in clinical practice merits further investigation.
Future research should include a cost-effectiveness analysis to identify acceptable
sensitivity and specificity, and an impact assessment to evaluate the utility
of these decision rules in clinical practice.
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