Transcript Introduction to Bone Densitometry Slideshow

Understanding
Bone Densitometry
www.ISCD.org
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Introduction
• Objective: To provide a basic
understanding of the principles of bone
densitometry
• Target audience: Non-densitometrist
healthcare professionals who wish to learn
about bone densitometry
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Copyright
• Slides with the ISCD logo in the lower left corner
are copyright © 2006 ISCD, and have been
reviewed and approved by the ISCD Scientific
Advisory Committee
• These ISCD slides may be reproduced and used
for any non-commercial educational purpose
• The ISCD logo must be removed, hidden, or
covered on any slides that are altered, edited or
added to the slide set
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Disclaimer
• ISCD slides are educational in nature and do not
constitute a medical or professional service
• Every effort has been made to assure that the
information provided is timely and accurate
• Due to the rapidly changing nature of the field,
some information presented may be outdated by
subsequent developments
• The ISCD shall not be held liable or responsible
to any person or entity for any loss or damage
alleged to be caused directly or indirectly by
information contained in these slides
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Outline
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What is bone density testing?
Why is it done?
Who should be tested?
When should it be repeated?
How is it interpreted?
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Why Should We Care?
• Osteoporosis is common - 44 million Americans
have osteoporosis or low bone mineral density
(BMD)
• Osteoporosis is serious - Fragility fractures are
associated with increased morbidity and mortality
• Osteoporosis is easy to diagnose - BMD testing
can detect osteoporosis before the first fracture
occurs
• Treatments are effective- Fracture risk can be
reduced by about 50%
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Definition of Osteoporosis
“A skeletal disorder characterized by
compromised bone strength predisposing to an
increased risk of fracture. Bone strength
reflects the integration of two main features:
bone density and bone quality. Bone quality
refers to architecture, turnover, damage
accumulation (e.g., microfractures), and
mineralization.”
NIH Consensus Development Panel on Osteoporosis Prevention, Diagnosis, and Therapy.
March 27-29, 2000. Published in JAMA 2001;285:785-795.
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Bone Densitometry
• Non-invasive test for measurement of BMD
• Major technologies
– Dual-energy X-ray Absorptiometry (DXA)
– Quantitative Ultrasound (QUS)
– Quantitative Computerized Tomography (QCT)
• Many manufacturers
• Numerous devices
• Different skeletal sites
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DXA
• “Gold-standard” for BMD measurement
• Measures “central” or “axial” skeletal sites: spine
and hip
• May measure other sites: total body and forearm
• Extensive epidemiologic data
• Correlation with bone strength in-vitro
• Validated in many clinical trials
• Widely available (about 15,000 DXA machines in
USA)
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DXA Technology
Detector (detects 2 tissue types - bone and soft tissue)
Very low radiation to patient.
Patient
Photons
Very little scatter radiation to
technologist
Collimator
(pinhole for pencil beam, slit for fan beam)
X-ray Source
(produces 2 photon energies with different attenuation profiles)
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Bone Density Testing
Is Done For Three Reasons
• To diagnose osteoporosis
• To predict fracture risk
• To monitor therapy
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What DXA Really Measures:
Bone Mineral Content (BMC)
In Grams and Area In cm2
• “Areal” BMD is calculated in g/cm2
• “T-score” compares the patient’s BMD
with the young-normal mean BMD and
expresses the difference as a standard
deviation (SD) score
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Which Skeletal Sites Should
Be Measured?
Every Patient
• Spine
– L1-L4
• Hip
– Total Hip
– Femoral Neck
Some Patients
• Forearm (33% radius,
1/3 radius)
– If hip or spine cannot be
measured
– Hyperparathyroidism
– Very obese
Use lowest T-score of these skeletal sites
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Why Not Use Ward’s Area?
• Using Ward’s area would overestimate the
prevalence of osteoporosis
• It is a small calculated area of the mid portion of
the femoral neck where BMD is the lowest - not
a well defined anatomic region
• Poor precision and accuracy
• Not part of WHO (World Health Organization)
criteria for BMD classification
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T-score
Patient’s BMD – Young-Adult Mean BMD
1 SD of Young-Adult Mean BMD
Example:
0.7 g/cm2 - 1.0 g/cm2
T-score =
0.1 g/cm2
= - 3.0
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Z-score
Patient’s BMD – Age-Matched Mean BMD
1 SD of Age-Matched Mean BMD
Low Z-score (less than -2.0) has been suggested
by some to increase likelihood of secondary
osteoporosis, however . . .
– This is not validated in clinical trials
– High index of suspicion for secondary causes of
osteoporosis is recommended for all patients
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WHO Diagnostic Classification
Classification
T-score
Normal
-1.0 or greater
Osteopenia
Between -1.0 and -2.5
Osteoporosis
-2.5 or less
-2.5 or less and fragility
Severe Osteoporosis
fracture
WHO Study Group. 1994.
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Diagnosis Caveats
• T-score -2.5 or less does not always mean
osteoporosis
– Example: osteomalacia
• Clinical diagnosis of osteoporosis may be
made with T-score greater than -2.5
– Example: atraumatic vertebral fracture with Tscore = -1.9
• Low T-score does not identify the cause
– Medical evaluation should be considered
– Example: celiac disease with malabsorption
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Why -2.5 for WHO Diagnosis?
Professor John Kanis says:
“Such a cutoff value identifies
approximately 30% of postmenopausal
women as having osteoporosis using
measurements made at the spine, hip or
forearm. This is approximately equivalent to
the lifetime risk of fracture at these sites.”
Kanis JA et al. J Bone Miner Res. 1994;9:1137.
Why T-score And Not Z-score for
WHO Diagnosis?
• T-score is related to bone strength
• T-score is related to fracture risk
• Using Z-scores would result in many
“normal” patients having fragility fractures,
and suggest that osteoporosis does not
increase with age
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Using T-scores vs. Z-scores
T-scores
• WHO diagnositic
classification in
postmenopausal women
and men age 50 and
older
• WHO classification with
T-score cannot be applied
to healthy premenopausal
women, men under age
50, and children
Z-scores
• For use in reporting BMD
in healthy premenopausal
women, men under age
50, and children
• Z-score -2.0 or less is
defined as “below the
expected range for age”
• Z-score above -2.0 is
“within the expected
range for age”
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T-score Discordance
• Different skeletal sites have different peak bone
mass at different times and lose bone at different
rates
• Different technologies
• Different regions on interest (ROIs)
• Different reference databases have different
means and SD (the hip is the only skeletal site
with a standardized reference database used by
all manufacturers – National Health and Nutrition
Examination Survey III)
Fracture Risk Doubles
With Every SD Decrease in BMD
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Relative
Risk
for
Fracture
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15
10
5
0
-5.0
-4.0
-3.0
-2.0
-1.0
Bone Density (T-score)
0.0
1.0
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Bone Density & Age vs. Fracture Risk
Age
50
80
70
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Ten Year
Fracture
Probability
(%)
30
60
20
50
10
0
1.0
0.5
0.0 -0.5 -1.0 -1.5 -2.0 -2.5 -3.0 -3.5 -4.0
Femoral Neck T-score
Probability of first fracture of hip, distal forearm, proximal humerus, and
symptomatic vertebral fracture in women of Malmö, Sweden.
Adapted from Kanis JA et al.
Osteoporosis Int. 2001;12:989-995.
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Treatment Guidelines
Summary of recommendations for pharmacologic therapy according to
Tscore from the National Osteoporosis Foundation (NOF) and the American
Association of Clinical Endocrinologists (AACE)
Patient Profile
T-score
NOF
AACE
No Risk Factors
Less than -2.0
-2.5 or less
Risk Factors†
Less than -1.5
-1.5 or less
† Fragility fracture, family history of fracture, cigarette smoking, low body
weight (<127 lbs.), etc.
National Osteoporosis Foundation 1998.
American Association of Clinical Endocrinologists 2001.
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Indications For Bone Density Testing
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All women age 65 and older
All men age 70 and older
Adults with a fragility fracture
Adults with a disease or condition associated with low bone
density
• Adults taking medication associated with low bone density
• Anyone being treated for low bone density to monitor
treatment effect
• Anyone not receiving therapy, in whom evidence of bone
loss would lead to treatment
Women discontinuing treatment should be considered for bone density
testing according to the indications listed above.
ISCD Position Development Conference 2003
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Payment For BMD Testing (USA)
Five Categories of Medicare Coverage
from the Bone Mass Measurement Act
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Estrogen-deficient women at clinical risk for osteoporosis
Individuals with vertebral abnormalities
Individuals receiving long-term glucocorticoid therapy
Individuals with primary hyperparathyroidism
Individuals being monitored to assess the response to or
efficacy of an FDA-approved osteoporosis drug therapy
Federal Register, Volume 63, Number 121, June 24, 1998.
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Why Do Serial BMD Testing?
• To monitor response to therapy by finding an
increase or stability of bone density
• To evaluate for non-response by finding loss
of bone density - suggesting the need for
reevaluation of treatment and evaluation for
secondary causes of osteoporosis
• To follow patients not being treated who are at
risk of bone loss, in order to determine if
treatment is needed
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When Should Repeat
BMD Testing Be Done?
• When expected change in BMD equals or
exceeds the “Least Significant Change” (LSC)
• Intervals between BMD testing should be
determined according to each patient’s clinical
status
– Consider one year after initiation or change of therapy
– Longer intervals once therapeutic effect is established
– Shorter intervals when rapid bone loss is expected
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How To Calculate LSC
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Scan 15 patients 3x each or 30 patients 2x each
Use patients typical of your practice
Reposition after each scan
Calculate SD for BMDs of each patient
Calculate Root Mean Square (RMS) SD in g/cm2
for the group of patients (this is the precision
error)
• Multiple RMS SD x 2.77 (this is the LSC with 95%
confidence)
• If change in BMD is equals or exceeds the LSC,
then the change is statistically significant
See “Precision Calculating Tool” at www.ISCD.org
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Least Significant Change
• Typical
– L1-L4: 3-4%
– Total proximal femur: 4-5%
• At one center
– L1-L4: 2.58% (.022 g/cm2)
– Total proximal femur: 4.63% (.036 g/cm2)
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Always Compare BMD
Never Compare T-scores
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BMD Values From Different
Manufacturers Are Not Comparable
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Different dual energy methods
Different calibration
Different detectors
Different edge detection software
Different regions of interest
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Advanced DXA Features
• Spine imaging (Vertebral Fracture
Assessment - VFA)
• Absolute fracture risk reporting
• Hip axis length (HAL)
• Combined hip / dual femur acquisition
• Remote interpretation and reporting tools
Peripheral BMD Testing
Accurate & Precise
• What it can do
– Predict fracture risk
– Tool for osteoporosis education
• What it cannot do
– Diagnose osteoporosis
– Monitor therapy
1. A “normal” peripheral test does not necessarily mean
that the patient does not have osteoporosis.
2. WHO criteria do not apply to peripheral BMD testing.
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The Osteoporosis Challenge
• To educate all patients on measures to
maintain good bone health
• To identify patients at high risk for
osteoporosis
• To use bone densitometry to detect low bone
density BEFORE a fracture occurs
• To use pharmacologic therapy appropriately
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ISCD
• The International Society for Clinical
Densitometry is a nonprofit professional
society established in 1993 to educate,
certify and establish standards in the field
of bone densitometry
• The ISCD does not endorse any company
or product involved with bone density
testing or the treatment of osteoporosis
• There are over 6,000 clinician and
technologist members worldwide
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Benefits Of ISCD Membership
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Journal of Clinical Densitometry (JCD)
SCAN® - Quarterly Newsletter
OsteoFlash® Web Updates
Blast E-mail Updates
Access to Members Only Section on Web
Discounts for Annual Meeting and Courses
Networking with others having similar
professional interests
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ISCD Bone Densitometry Course
• Comprehensive 1½ day CME/CE course
with separate tracks for clinicians and
technologists
• Essential education for bone densitometry
center staff
• Preparation for ISCD Certification Exam
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ISCD Certification
• Personal recognition of bone densitometry
skills
• Demonstration of proficiency in bone
densitometry for colleagues and managed
care organizations
• Marketing advantage for centers with
certified staff
• Required for reimbursement by some
managed care organizations
Quality Bone Mineral
Density Testing
www.ISCD.org
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West Hartford, CT 06117-2507 USA
Tel 860-586-7563  Fax 860-586-7550  E-mail [email protected]
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