Understanding Bone Densitometry www.ISCD.org

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

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%

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.

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

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)

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)

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

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

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

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

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/cm2 - 1.0 g/cm2 0.1 g/cm2 = - 3.0

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

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. 1994.

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

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.

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

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”

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 Relative Risk for Fracture Exponential Relationship Bone Density (T-score)

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;12:989-995.

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 1998. American Association of Clinical Endocrinologists 2001.

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

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.

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

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.

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 www.ISCD.org

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)

Never Compare T-scores Always Compare BMD Never Compare T-scores

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

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

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.

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

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

Benefits Of ISCD Membership 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

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

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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