Part 1: Understanding Osteoporosis

Yes, the correct answer is "dual energy x-ray absorptiometry, more commonly known as a DEXA scan."

However, the other methods listed* are all viable options:

Conventional radiographs of the spine would be the most widely available method, however they are insensitive indicators of bone loss, since they cannot detect osteoporosis until a person loses 30% or even 40% of their bone mass.

Quantitative computed tomography can measure trabecular bone density of the spine by directly assessing bone volume, however the radiation dose is substantially higher than other methods that are available to measure bone density. The average scan time is 10 - 20 minutes and the costs can run as high as $500 per scan.

Radiographic absorptiometry only measures a peripheral site (the fingers).

Considered by many to be the "gold standard" method, the DEXA is a new and improved method to determine both bone mineral content and bone mineral density, and is a two-dimensional projection system that utilizes an x-ray tube source. It can measure bone mineral in the peripheral appendicular skeleton which is composed mainly of cortical bone, and in the axial skeleton which is made up of varying proportions of trabecular and cortical bone.

You'll recall in our discussion of trabecular bone, that it is lost more than cortical bone and has a high surface-to-volume ratio. It is usually the first choice for screening, so consequently sites which are highly trabeculated such as the spine and hip are usually scanned since they will provide better information on bone loss than in sites such as the forearm. The average scan time is 5 minutes and the cost is about $75 to $150 per scan.

Bone mineral density tests are quick and painless and are covered by Medicare for people age 65 or older who are considered to be at risk. They provide physicians with a measurement called a T-score, which is a number value that compares a person's bone density to that which is considered optimal. If a T-score is a negative number, such as -1, -2, -2.5, it indicates that bone loss has occurred. The more negative a number is, the greater the risk of fracture. A score of -2.5 is considered a diagnosis of osteoporosis.

* Source - Osteoporosis: A Guide to Prevention, Early Detection and Treatment, VA Dept. of Health