1. Understanding Bone Densitometry

2. 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

3. 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

4. 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Due to the rapidly changing nature of the field, some information presented may be outdated by subsequent developments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

5. Outline What is bone density testing? Why is it done?
Who should be tested?
When should it be repeated?
How is it interpreted?

6. 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%

7. 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, Published in JAMA 2001;285:

8. 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

9. 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)

10. DXA Technology
Detector (detects 2 tissue types - bone and soft tissue)
Very low radiation to patient.
Very little scatter radiation to technologist
Patient
Collimator (pinhole for pencil beam, slit for fan beam)
Photons
X-ray Source (produces 2 photon energies with different attenuation profiles)

11. Bone Density Testing Is Done For Three Reasons
To diagnose osteoporosis
To predict fracture risk
To monitor therapy

12. 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

13. 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

14. 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

15. Patient’s BMD – Young-Adult Mean BMD 1 SD of Young-Adult Mean BMD
T-score
Patient’s BMD – Young-Adult Mean BMD
1 SD of Young-Adult Mean BMD
Example:
T-score =
0.7 g/cm g/cm2
0.1 g/cm2 =

16. 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

17. WHO Diagnostic Classification
T-score
Normal
-1.0 or greater
Osteopenia
Between -1.0 and -2.5
Osteoporosis
-2.5 or less
Severe Osteoporosis
-2.5 or less and fragility fracture
WHO Study Group

18. 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 T-score = -1.9
Low T-score does not identify the cause
Medical evaluation should be considered
Example: celiac disease with malabsorption

19. Kanis JA et al. J Bone Miner Res. 1994;9:1137.
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.

20. 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

21. Using T-scores vs. Z-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”

22. 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)

23. Fracture Risk Doubles With Every SD Decrease in BMD
Relative Risk
for Fracture
Exponential Relationship
Bone Density (T-score)

24. Bone Density & Age vs. Fracture Risk
Ten Year Fracture Probability (%)
Age 80 70 60 50
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:

25. Treatment Guidelines Patient Profile T-score NOF AACE No Risk Factors
Summary of recommendations for pharmacologic therapy according to T-score 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 American Association of Clinical Endocrinologists 2001.

26. Indications For Bone Density Testing
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

27. Payment For BMD Testing (USA)
Five Categories of Medicare Coverage
from the Bone Mass Measurement Act
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.

28. 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

29. 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
typically 1year after initiation or change of therapy is appropriate, with longer intervals once therapeutic effect is established. In conditions associated with rapid bone loss, such as glucocorticoid therapy, more often is appropriate.

30. See “Precision Calculating Tool” at www.ISCD.org
How To Calculate LSC
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

31. 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)

32. Never Compare T-scores
Always Compare BMD
Never Compare T-scores

33. BMD Values From Different Manufacturers Are Not Comparable
Different dual energy methods
Different calibration
Different detectors
Different edge detection software
Different regions of interest

34. 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
Lateral Vertebral Assessment
Instant Vertebral Assessment
Dual Vertebral Assessment

35. Peripheral BMD Testing Accurate & Precise
What it can do
Predict fracture risk
Tool for osteoporosis education
What it cannot do
Diagnose osteoporosis
Monitor therapy
A “normal” peripheral test does not necessarily mean that the patient does not have osteoporosis.
WHO criteria do not apply to peripheral BMD testing.

36. 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

37. 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

38. Benefits Of ISCD Membership
Journal of Clinical Densitometry (JCD)
SCAN® - Quarterly Newsletter
OsteoFlash® Web Updates
Blast Updates
Access to Members Only Section on Web
Discounts for Annual Meeting and Courses
Networking with others having similar professional interests

39. 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

40. 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

41. Quality Bone Mineral Density Testing

42. Tel 860-586-7563  Fax 860-586-7550  E-mail iscd@iscd.org
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West Hartford, CT USA
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