Bone Mineral Density TestingBone Mineral Density Testing

March 29, 2007March 29, 2007

IntroductionIntroduction

Osteoporosis is a systemic skeletal disorder Osteoporosis is a systemic skeletal disorder characterized by decreased bone mass and characterized by decreased bone mass and deterioration of bony microarchitecture deterioration of bony microarchitecture

This decrease in bone mineral density (BMD) This decrease in bone mineral density (BMD) results in fragile bones and an increased risk for results in fragile bones and an increased risk for fracture with even minimal trauma fracture with even minimal trauma

Prior to testing, osteoporosis was clinically silent Prior to testing, osteoporosis was clinically silent until a fracture occurreduntil a fracture occurred

PathophysiologyPathophysiology

Decreased bone mineral density is a result Decreased bone mineral density is a result of a combination of genetic and of a combination of genetic and environmental factors that affect both peak environmental factors that affect both peak bone mass and the rate of bone loss bone mass and the rate of bone loss

These factors include medications, diet, These factors include medications, diet, race, sex, lifestyle, and physical activity race, sex, lifestyle, and physical activity

FrequencyFrequency

Approximately 10 million people have Approximately 10 million people have osteoporosis. Another 14-18 million have osteoporosis. Another 14-18 million have osteopenia (low bone mass) osteopenia (low bone mass)

Approximately 1.5 million fractures per Approximately 1.5 million fractures per year in the United States are attributed to year in the United States are attributed to osteoporosis, and more than 37,000 osteoporosis, and more than 37,000 people die from subsequent fracture-people die from subsequent fracture-related complicationsrelated complications

So Who Do We Test?So Who Do We Test?

Postmenopausal women older than 65 yearsPostmenopausal women older than 65 yearsPostmenopausal women younger than 65 years who Postmenopausal women younger than 65 years who have 1 or more risk factor have 1 or more risk factor Postmenopausal women who present with fragility Postmenopausal women who present with fragility fractures fractures Women who are considering therapy in which BMD will Women who are considering therapy in which BMD will affect that decision affect that decision Women who have been on hormone replacement Women who have been on hormone replacement therapy (HRT) for prolonged periods therapy (HRT) for prolonged periods Men who experience fractures after minimal trauma Men who experience fractures after minimal trauma People with evidence of osteopenia on radiographs or a People with evidence of osteopenia on radiographs or a disease known to place them at risk for osteoporosis disease known to place them at risk for osteoporosis

Lab StudiesLab Studies

Levels of serum calcium, phosphate, and Levels of serum calcium, phosphate, and alkaline phosphatase are usually normal in alkaline phosphatase are usually normal in persons with primary osteoporosis, persons with primary osteoporosis, although alkaline phosphatase levels may although alkaline phosphatase levels may be elevated for several months after a be elevated for several months after a fracture fracture

It is important to also check thyroid It is important to also check thyroid function, and testosterone levels in menfunction, and testosterone levels in men

Imaging StudiesImaging Studies

First, obtain plain radiographs if a First, obtain plain radiographs if a decrease in bone mineral density is decrease in bone mineral density is suspectedsuspected

Osteopenia may be apparent as Osteopenia may be apparent as radiographic lucency but is not always radiographic lucency but is not always noticeable until 30% of bone mineral is lostnoticeable until 30% of bone mineral is lost

Plain radiography is not as accurate as Plain radiography is not as accurate as BMD testing BMD testing

BMD ImagingBMD Imaging

BMD tests are usually done on bones that BMD tests are usually done on bones that are likely to break as a result of are likely to break as a result of osteoporosis like the lower spine and hiposteoporosis like the lower spine and hipCan also be done on the wrist or heelCan also be done on the wrist or heelDevices that measure BMD include:Devices that measure BMD include:– Quantitative computed tomography Quantitative computed tomography – Dual-energy x-ray absorptiometry (DEXA) Dual-energy x-ray absorptiometry (DEXA) – Quantitative ultrasonography Quantitative ultrasonography – Radiogrammetry Radiogrammetry

Quantitative Computed Quantitative Computed TomographyTomography

Quantitative computed tomography measures Quantitative computed tomography measures BMD as a true volume density in g/cm3, which is BMD as a true volume density in g/cm3, which is not influenced by bone size. not influenced by bone size. This technique can be used for both adults and This technique can be used for both adults and children. children. Disadvantages in that (1) it only determines Disadvantages in that (1) it only determines bone density at the spine, (2) osteophytes can bone density at the spine, (2) osteophytes can interfere with measurement, and (3) it is interfere with measurement, and (3) it is associated with significant radiation exposure associated with significant radiation exposure and high cost and high cost

DEXADEXA

Dual-energy x-ray absorptiometry requires less radiation, Dual-energy x-ray absorptiometry requires less radiation, is less expensive, and has better reproducibility than is less expensive, and has better reproducibility than quantitative computed tomographyquantitative computed tomographyCan also measure bone density at the spine and the hip. Can also measure bone density at the spine and the hip. It has become the standard method for determining bone It has become the standard method for determining bone density. density. This method can be used in both adults and childrenThis method can be used in both adults and childrenConfounding factors in DEXA results interpretation Confounding factors in DEXA results interpretation (falsely high bone density) include spinal fractures, (falsely high bone density) include spinal fractures, osteophytosis, and extraspinal (eg, vascular) calcification osteophytosis, and extraspinal (eg, vascular) calcification Peripheral DEXA can be used to measure BMD in the Peripheral DEXA can be used to measure BMD in the wristwrist

Quantitative UltrasonographyQuantitative Ultrasonography

Quantitative ultrasonography of the Quantitative ultrasonography of the calcaneus can be used for general calcaneus can be used for general screeningscreening

However, this is not as accurate as other However, this is not as accurate as other methods and thus is less useful in methods and thus is less useful in following response to treatmentfollowing response to treatment

Its advantages include low cost, portability, Its advantages include low cost, portability, and lack of ionizing radiation and lack of ionizing radiation

RadiogrammetryRadiogrammetry

Radiogrammetry, used to measure cortical Radiogrammetry, used to measure cortical dimensions, is usually performed on the dimensions, is usually performed on the hand, specifically the second metacarpalhand, specifically the second metacarpalIt is useful in assessing BMD in children It is useful in assessing BMD in children and is the simplest and least expensive and is the simplest and least expensive methodmethodDisadvantages are that it is not as precise Disadvantages are that it is not as precise as DEXA and, therefore, is less sensitive as DEXA and, therefore, is less sensitive for detecting changes over time for detecting changes over time

What Are The Results?What Are The Results?

Results are reported as two values, T and Z Results are reported as two values, T and Z scoresscores

T scores are the number of standard deviations T scores are the number of standard deviations above or below what is normally expected in a above or below what is normally expected in a healthy young adult of the same sexhealthy young adult of the same sex

Z score is the number of standard deviations Z score is the number of standard deviations above or below what is normally expected for above or below what is normally expected for someone of the same age, sex, weight, and someone of the same age, sex, weight, and ethinic originethinic origin

T ScoreT Score

Above -1 indicates the bone density is Above -1 indicates the bone density is normalnormal

Between -1 and -2.5 indicates bone Between -1 and -2.5 indicates bone density is below normal, or osteopeniadensity is below normal, or osteopenia

Below -2.5 indicates osteoporosisBelow -2.5 indicates osteoporosis

DEXA ImagesDEXA Images

BMD Score ReportBMD Score Report

Z ScoreZ Score

The Z score is help ful because it may The Z score is help ful because it may suggest that the patient may have a suggest that the patient may have a secondary form of osteoporosis unrelated secondary form of osteoporosis unrelated to normal aging which is causing to normal aging which is causing decreased BMDdecreased BMD

A score less than -1.5 should make you A score less than -1.5 should make you investigate the cause of decreased BMD investigate the cause of decreased BMD

Another Report CardAnother Report Card

For example, if the T-score is -2.0, the BMD is lower For example, if the T-score is -2.0, the BMD is lower than average by two standard deviations. If the Z-score than average by two standard deviations. If the Z-score is -0.5, your bone density is less than the norm for is -0.5, your bone density is less than the norm for

people your age by one-half of a standard deviationpeople your age by one-half of a standard deviation

QCT QCT

QCTQCT

QCT isolates metabolically active QCT isolates metabolically active trabecular bone for greater anatomic trabecular bone for greater anatomic accuracy than other methods accuracy than other methods

A series of axial scans are taken with the A series of axial scans are taken with the patient lying on a calibration phantom patient lying on a calibration phantom

Other TestsOther Tests

As mentioned earlier, ultrasound and As mentioned earlier, ultrasound and radiogrammetry can be used as wellradiogrammetry can be used as well

These are not as accurate in determining These are not as accurate in determining BMD loss but have advantages like less BMD loss but have advantages like less radiation, smaller equipment, and they radiation, smaller equipment, and they measure BMD using smaller bonesmeasure BMD using smaller bones