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Journal of the Academy of Hospital Administration

Bone Densitometry: An Overview

Author(s): Reena Kumar*, Nikhil Tandon*

Vol. 15, No. 2 (2003-07 - 2003-12)


Osteoporosis is a chronic condition characterized by low bone mass and architectural deterioration resulting in, increased bone fragility and increased risk of bone fracture. Although considered a disease of frail elderly individuals, it disproportionately affects a large number of women. According to the WHO, twenty five million Americans have osteoporosis of which 80% are women. One out of every 40 men has osteoporosis. The key to successful management of osteoporosis is early detection and quick and prolonged treatment. This means measuring, testing, screening, and diagnosing low bone mass in women and men early in their lifetime so that effective treatment can be started on time to stop osteoporosis. Osteoporosis, which ravages so many women and men, can now be prevented by early diagnosis with the help of state of the art Bone densitometry equipment. This article explains it's indications, the principle of bone densitometry, safety and radiation hazards to patients, techniques, cost and benefits.


The currently accepted definition of osteoporosis is "a systemic skeletal disease characterized by low bone mass and micro- architecture deterioration of bone tissue, with a consequent increase in bone fragility and susceptibility to fracture risk"1 Osteoporosis is a " silent " disease that can become deforming and painful. The clinical significance of osteoporosis lies in the fractures, and is therefore a major health care problem. Common sites of fracture are the spine, wrist and hip, but when bone loss occurs, all bones are at high risk. Osteoporotic fractures occurring at the spine and the forearm are associated with significant morbidity, but the most serious consequences arise in patients with hip fracture, which is associated with a significant increase in mortality (15-20%) particularly in elderly men and women.2

Today, 250 million women worldwide have osteoporosis. By the year 2020, the number of women affected will double. A Gallup survey in USA of women aged 45-75 years indicated that 3 out of 4 women have never spoken to a doctor about osteoporosis. In USA, an average primary care doctor sees 54 women a week over the age of 50. Of these 54 women, 30% have osteoporosis. Osteoporosis leads to 1.5 million fractures each year. These include 300,000 hip fractures, 250,000 wrist fractures and 500,000 spinal fractures. 50% of the people suffering from a hip fracture won't walk again and 20% of them would die within one year. A women's risk of developing a hip fracture is equal to her combined risk of developing breast, uterine and ovarian cancer. $18 billion is spent on treating those fractures3. Thus, it is obvious that osteoporosis silently leads to tremendous orthopaedic problems in women and puts heavy burden on the health budget. Fortunately, much of it can be detected in time and avoided by therapeutic intervention.4

The key to preventing osteoporotic fractures in women and men is early detection, diagnosis and treatment. This means measuring, testing, screening, detecting and diagnosing low bone mass in women and men early in their lifetimes, so that effective treatment can stop the osteoporosis. One of the key developments in preventing and treating osteoporosis is its early diagnosis by Bone densitometry, which is available at many centres today3.

Diagnosing Osteoporosis

Several approaches have been utilized to diagnose osteoporosis on the basis of bone mineral density measurements5. The most straightforward is to define a fracture threshold, namely the cut-off for BMD, which captures most patients with osteoporotic fractures. This can be variously and arbitrarily set, for example at the mean or 1 or 2 standard deviations (SD) above the mean value of patients with osteoporotic fracture, or at a set point below the mean of the young adult reference range. The setting of the fracture threshold depends not only on the site measured and technique used but also on other factors such as the site of interest, age and sex.

In adult women, the cut off value of 2.5 SD below the average of the healthy young adult range is appropriate to satisfy many of these criteria, particularly for hip fracture6. More than one cut off can be chosen to denote the severity of disease. The four general diagnostic categories established for adult women by the European Foundation for Osteoporosis and Bone Disease, is accepted by the National Osteoporosis Foundation of United States and the World Health Organization (WHO 1994).

World Health Organization definitions of T and Z scores

The World Health Organization has defined osteoporosis and osteopenia based on these values. The T-score is the number of standard deviation from the mean (average) value.

  • Normal bone: T-score better than -1
  • Osteopenia: T-score between -1 and -2.5
  • Osteoporosis: T-score less than -2.5

Established osteoporosis includes the presence of a non-traumatic fracture. The diagnostic categories above identify 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 any of these sites. When measurements are made at the one site alone, then the prevalence is 15-20%, which is comparable to the lifetime risk of a single osteoporotic fracture such as a hip fracture.

Because the distribution of values for BMD in the young healthy population is Gaussian, the incidence of osteoporosis increases exponentially after the age of 50 years as is also the case for many osteoporosis related fractures.

What is Bone Densitometry?

Bone densitometry is a non-invasive technology that is used to measure bone mass. Bone mass, simply put, is the weight of the skeleton, overall or in specific regions. It is most important to measure bone mass in the spine, hips, and arms because these are the areas most likely to fracture when bone mass is low. The amount of bone you have in your skeleton determines how strong it is and how much trauma or force it can withstand before it fractures. Bone densitometry measurements are helpful in estimating the risk of fracture and to assess the result of treatment7.

Bone Densitometry Machine

pic of bone densiometry machine

Source: All India Institute of Medical Sciences

How is it done (Techniques)?

There are numerous methods of assessing bone densitometry which differ from each other in the technology used to measure the bone mass. The most commonly used method for measuring bone mass is called Dual Energy X-Ray Absorptiometry, or DEXA. To measure bone mass with a DEXA machine, the person lies on a flat padded table and remains motionless while the "arm" of the instrument passes over the whole body or over selected areas. While the measurement is performed, a beam of low-dose x-rays from below the table passes through the area being measured. A device in the instrument's arm detects these x-rays. The machine converts the information received by the detector into an image of the skeleton and analyzes the quantity of bone contained in the skeleton The results are usually reported as "Bone Mineral Density (BMD)" which reflect the amount of bone per unit of skeletal area7. For the spine measurement, the person's lower legs rest on a styrofoam cube with the hips flexed. For the hip measurement, the toes are placed in a "pigeon-toed" position to rotate the hips and provide the largest projected area to measure. For the arm measurement, the person sits on a chair beside the machine and places an arm into a holding device while the measurement is taken. For a total body measurement, which provides individual measurements of the legs, the trunk, the pelvis, the ribs, the arms and the skull, the person, simply lies flat and motionless11.

It is important to remember that, if the patient moves while the measurement is taking place, errors can occur. Usually it is not too difficult for the person to remain motionless because, using the latest equipment, each measurement requires less than a minute to perform7.

How can you get Bone densitometry measurements?

To obtain a bone density measurement, a physician should refer the patient. While some bone densitometry centers perform measurements without a doctor's request, it is better to have checkup and referral from your personal physician who will interpret the results and provide treatment based on that, in the context of your overall medical situation7.

When is Bone densitometry measurement indicated?

Patients recommended for Bone mineral density measurements6:

Post-menopausal women with at least one additional risk factor (other than menopause).

All women older than 65 regardless of risk factors.

Post-menopausal women who present with fractures.

Women considering therapy for osteoporosis, if bone mineral density (BMD) testing would affect the decision.

Women who have been on hormone replacement therapy (HRT) for prolonged periods of time.

How often should the test be performed?

Bone densitometry measurements are usually performed not more than once a year in adults. Bone mass changes relatively slowly in most adults. It is not useful to perform measurements when the expected changes in bone mass are smaller than the machine can accurately detect8.

What preparation? Does it hurt? Safety and radiation hazards?

No preparation is necessary for Bone Densitometry. The patient doesn't have to take any pill or any injection or swallow any medicines (e.g. barium) or any radionuclide material prior to or at the time of scan.

Bone densitometry is not painful. There is no needle stick involved and one cannot feel anything when the x-rays pass through the body. The hardest part is remaining still for the minute or so when the measurement is performed. Unlike an MRI DEXA instrument does not enclose the patient.

DEXA technology is quite safe. Radiation exposure is exceedingly small, about the equivalent of playing outdoors all day on a summer day or flying across the United States in a jet plane. Using DEXA, a person receives less than 10% of the radiation received in a standard chest x-ray. State regulatory agencies permit routine measurement of healthy children. Spine or femur measurements take approximately two to five minutes while total body measurements take approximately ten to fifteen minutes13.

What does it cost?

In Government Institutions like All India Institute of Medical Sciences, New Delhi; Bone Densitometry costs Rs 400, Rs 600, Rs 800 for single, two, three site study and Rs 1000 for whole body scan. In Private Institutions in Delhi, like Apollo hospital and Max Health care, it costs Rs 1500-Rs 2000 for single site and Rs 3000-Rs 3500 for whole body scan.

In USA, it costs between $75.00 and $150.00, depending on which machine is used and what areas of the skeleton are measured7. Most metropolitan areas have several densitometers.8

What are the benefits of bone densitometry scan?

Bone densitometry is a non-invasive, accurate, inexpensive way of detecting osteoporosis. The procedure takes 15-30 minutes and does not require undressing. A bone densitometry scan is beneficial for any age or gender, provides early detection that other tests miss, can measure multiple sites of the body to determine the most appropriate treatments, can estimate fracture risk and is easily administered with a low radiation dose that is roughly equivalent to a cross-country airline flight.12

Techniques for measuring bone mass or density

Currently the most widely used technique is DEXA (Dual Energy X-ray Absorptiometry). This is the method used to characterize fracture risk in large epidemiological studies and to determine efficacy in the recent large clinical trials14.

Understanding the Results of Bone Mineral Density Tests: T-score and Z-score

The bone densitometry will measure your bone mineral density (BMD). It will also compare your measurements to a reference population based on age, weight, sex and ethnic background. The normative data produced by this machine is generated by the WHO using western caucasian subjects. .These may not be applicable to ethnic Indian. The referring clinician may interpret these data in the context of the subject is clinical and biochemical data. This information will be used by the physician in making a diagnosis about bone status and fracture risk.

Bone mineral density (BMD) tests are performed to determine whether a patient has osteoporosis or osteopenia, a low bone mass that puts her at risk for osteoporosis. The World Health Organization (WHO) established the criteria for determining the T-score. The T score is the number of standard deviations from the mean (average) values.

The scan information of lumbar spine done by Hologic machine installed at All India Institute of Medical Sciences on three different patients shows the following results.

Scan of Patient X

image of xray and graph

Reference curve and scores matched to a Male; Source: Hologic

DXA Results Summary:

Region Area BMC BMD T Z
  (cm2) (g) g/cm2 Score Score
1.1 12.87 13.65 1.061 1.2 2.5
1.2 13.95 14.33 1.028 0 1.4
1.3 15.84 17.47 1.103 0.2 1.6
1.4 20.15 22.52 1.118 0.1 1.5
total 62.80 67.98 1.082 0.3 1.7

Total BMD CV 1.0%, ACF=1.26, BCF= 1.005, TH= 5.788
WHO Classification: Normal
Fracture Risk: Not Increased

Scan of Patient Y

image of xray and graph

DXA Results Summary:

Region Area BMC BMD T Z
  (cm2) (g) g/cm2 Score Score
1.1 9.06 6.69 0.739 -1.7 -0.5
1.2 10.98 10.80 0.984 -0.4 0.9
1.3 11.81 10.56 0.894 -1.7 -0.4
1.4 13.88 12.80 0.922 -1.8 -0.4
total 45.72 40.85 0.894 -1.4 -0.1

Total BMD CV 1.0%, ACF=1.26, BCF= 1.005, TH= 5.788
WHO Classification: Osteopenia
Fracture Risk: Increased

Scan of Patient Z

image of xray and graph

Reference curve and scores matched to a Male
Source: Hologic
Source All India Institute of Medical Science

DXA Results Summary:

Region Area BMC BMD T Z
  (cm2) (g) g/cm2 Score Score
1.1 12.74 5.86 0.460 -5.0 -5.0
1.2 14.66 8.73 0.596 -4.5 -4.5
1.3 17.62 9.26 0.526 -5.2 -5.2
1.4 17.51 9.72 0.555 -5.4 -5.4
total 62.54 33.58 0.537 -5.0 -5.0

Total BMD CV 1.0%, ACF=1.026, BCF= 1.005, TH= 5.796
WHO Classification: Osteoporosis
Fracture Risk: High

According to WHO classification, patient X with T-score 0.3 and Z-score of 1.7 shows Normal scan. and there is no risk of fragility fracture. Patient Y, with T-score -1.4 and Z-score of - 0.1 shows. Ostopaenia, and there is an increased risk of fracture. Patient Z, with T-score = 5 and Z-score = 5 shows Osteoporosis, and there is high risk of fracture.

Ultrasound is a new technique which appears to offer a more cost-effective method of screening bone mass. Ultrasound measurements are usually performed at the calcaneus and it is not possible to measure sites of osteoporotic fracture such as the hip or spine. Adding an ultrasound measurement to a DEXA does not improve the prediction of fractures. Although some have said that ultrasound measures the "quality" of bone, more careful studies suggest that it mainly measures the bone mass14. This technique is not yet approved for diagnosis of osteoporosis/osteopenia.

Quantitative computed tomography (QCT) of the spine must be done following strict protocols in laboratories that do these tests frequently, as in community settings, the reproducibility is poor. The QCT measurements decrease more rapidly with aging14.


Apart from Dexa, Ultrasound and QCT, numerous other techniques are also available. These techniques and the area that they scan are as follows: can measure bone density at the hand, radius or ankle. These include single energy absorptiometry, metacarpal width or density from hand x rays. Magnetic resonance imaging is a new method of measuring bone density14.

SXA (single Energy X-ray Absorptiometry) measures the wrist or heel.

PDXA (Peripheral Dual Energy X-ray Absorptiometry) measures the wrist, heel or finger.

RA (Radiographic Absorptiometry) uses an X-ray of the hand and a small metal wedge to calculate bone density

DPA (Dual Photon Absorptiometry) measures the spine, hip or total body ( Old and now obsolete method)

SPA (Single Photon Absorptiometry) measures the wrist ( Old and now obsolete method)

The most approved technique for measuring bone mass or density is DXA.

The accuracy of bone mineral density test is high, ranging from 85% to 99%. According to physicians, QCT is the most accurate test for measuring BMD and ultrasound is the least accurate of the tests. However, QCT is not widely available and delivers more radiation to the patient than DEXA. DEXA is the most widely available and used BMD test and its accuracy is in between those of QCT and ultrasound.


Osteoporosis results in more than one million hip, spine, and wrist fractures annually in USA. Osteoporosis is a major public health problem for which effective action has to be taken. Early diagnosis is therefore essential to estimate the severity of disease, predict the subsequent clinical course and prognosis and to initiate treatment. Osteoporotic fractures, which are the main clinical presentation of osteoporosis, occur relatively at late stage of disease when there has been considerable bone loss. A key factor in this success has been the availability of new and improved equipment to measure bone density. Using a bone densitometer, physicians can measure patient bone density and follow it over time. If the patient's bone density is low, or decreases at an abnormally fast rate, the patient may be at risk for osteoporosis and osteoporotic fractures. It is therefore necessary to identify potential patients who can be appropriately managed to reduce their chances of sustaining fracture, which can be done in 3 ways.

  1. Clinical risk assessment
  2. Bone densitometry measurement
  3. Assessment of biochemical markers of bone turnover9

Bone densitometry by DEXA or other methods can be useful in the management of patients with osteoporosis. The procedure is easy, noninvasive, safe, and convenient. The technology is accessible to almost everyone. Though it is expensive, it is becoming an integral part of the medical management of patients at risk for osteoporosis.


  1. Anon (1993) Consensus development conference: diagnosis prophylaxis and treatment osteoporosis. Am J Med; 94: 646-650.
  2. Kanis JA (1994) Osteoporosis: Osteoporosis and its consequences.
  3. http://www. Bone
  4. National Osteoporosis Foundation / World Health Organization.
  5. Kanis JA(1990) Osteoporosis and Osteoporosis and Osteopenia. J Bone Mineral Res; 5, 209-211.
  6. Newton John HF, Morgan DB (1970). The loss of bone with age, Osteoporosis, and fractures clin Orthop; 71; 229- 252.
  8. National Institutes of Health Osteoporosis and related bone disease National Resource Centre, Washington, DC.
  9. Manual of Bone Densitometry measurements 2000 J.N. Fordham.
  10. WHO (1994) Assessment of Osteoporotic Fracture Risk and its role in screening for post menopausal osteoporosis WHO technical report series.
  11. Dalen N, Hell Strom L, Jacobson B (19976) Bone Mineral Content and Mechanical Strength of the femoral neck. Acta Orth op Scand, 47: 503-508.

* Sr. Resident, Deptt. of Hospital Administration A.I.I.M.S., New Delhi
** Additional Professor, Deptt. of Endocrinology A.I.I.M.S., New Delhi

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