How osteoporosis can be detected

You've hit menopause but you're wary of the O-word. You know the dangers of osteoporosis, but don’t know how to go about the tests. Fear not. Here's a guide to help you combat this debilitating bone disease:

Eisha Sarkar

What's osteoporosis?
It results from progressive bone loss and is associated with an increased risk of fracture. In scientific terms, the bone mineral density (BMD) is reduced and the bone structure is disrupted.
Dr Dinesh Upadhyaya, a senior sports medicine expert at the Tata Main Hospital, Jamshedpur says, "Osteoporosis is an epidemic. Only, we can't classify it as one because we haven't been able to test so many people."
Osteoporosis is most common in women after menopause. Also, it may occur in a person who suffers from hormonal disorders and other chronic diseases or as a result of medications, specifically glucocorticoids.

Under the scanner
All women aged 65 and over
Younger postmenopausal women who have one or more risk factors
Postmenopausal women who have suffered a fragility fracture to confirm the diagnosis and determine disease severity.

Check your bone density
"Most people don't know they have osteoporosis till they actually get a fracture from a minor fall," says Dr Upadhyaya. While screening for serum calcium may confirm the cause for certain symptoms of osteoporosis (bend in the spine, loss of height and chronic back pain), its diagnosis involves a measurement of BMD, says Dr Upadhyaya. This can be done with the help of the following tests:

1. Radiographic Measurement
How it's done: Bone density is measured on plain radiographs (X-rays).
Precision: Low. The loss of bone density is not apparent on a plain X-ray until approximately 40% of the bone is lost.

2. Radiographic absorptiometry
How it's done: An X-ray of the hand is taken, incorporating an aluminum reference wedge. The X-ray is then analysed, and the density of the bone is compared to the density of the wedge.
Precision: Low

3. Single-Photon absorptiometry (SPA)
How it's done: A single-energy photon beam is passed through bone and soft tissue (usually the wrist) to a detector. The amount of mineral in the path is then quantified.
Precision: The measurements are accurate, and the test usually takes about 10 minutes.

4. Dual-Photon Absorptiometry (DPA)
How it's done: It uses a photon beam that has two distinct energy peaks. One energy peak is absorbed more by the soft tissue. The other by bone. The soft-tissue component is subtracted to determine the BMD. DPA allows for BMD measurements of the spine and proximal femur.
Precision: Although DPA is accurate for predicting fracture risk, the precision is poor because of decay of the isotope.

5. Dual-Energy X-ray Absorptiometry (DEXA)
How it's done: It works in a similar fashion to DPA, but uses an X-ray source instead of a radioactive isotope. This technique is superior to DPA because the radiation source does not decay and the energy stays constant over time. DEXA is the "gold standard" for BMD measurement.
Precision: DEXA scans are extremely precise. Precision in the range of 1% to 2% has been reported. It can be used to monitor changes in bone density in patients undergoing treatments. Scan times for DEXA are much shorter than for DPA, and the radiation dose is very low.

6. Quantitative Computed Tomography (QCT)
How it's done: QCT is unique in that it provides for true three-dimensional imaging and reports BMD as true volume density measurements.
Precision: High. The advantage of QCT is the ability to isolate an area of interest from surrounding tissues. QCT can, therefore, localize an area in a vertebral body of only trabecular bone, leaving out the elements most affected by degenerative change and sclerosis. The radiation dose with QCT is about 10 times that of DEXA, and QCT tests may be more expensive than DEXA.

7. Peripheral Bone Density Testing
How it's done: Low-cost portable devices can determine BMD at peripheral sites such as wrist and fingers. This allows for BMD assessment in a population who otherwise would not be able to have the test. These machines are considerably less expensive.
Precision: Although the machines are accurate, doubts have been raised about their precision. As only one site is tested, low bone density in the hip or spine may be missed. This may be a problem because of differences in bone density between different skeletal sites. Peripheral machines may not be good enough to monitor patients undergoing treatment for osteoporosis.

In postmenopausal women up to 65 years, the most accurate site to measure BMD is the spine.
In women older than 65 years, BMD is similar across the skeleton; therefore, it may not make a difference which site is measured.

I had written the story on tests for osteoporosis while I was in Jamshedpur. Check it out:
http://ms.timesofindia.com/ads/womensday09/wd_tw/menopause.html