Osteoporosis - Frequently Asked Questions

FAQs


Rheumatology Division,
Hospital for Special Surgery

  1. What is a DXA test?
  2. What does my DXA T score mean?
  3. So what DXA score means I have osteoporosis?
  4. What kind of calcium should I take?
  5. When do I need to take medication?
  6. How do drugs for osteoporosis work?

What is a DXA test?
A DXA test, which stands for Dual-Energy X-ray Absorptiometry, is a low-level x-ray measuring important bone sites, and it is the most commonly used technique to assess bone density.  It is painless, non-invasive, and takes about 10 minutes.

What does my DXA T score mean?
The DXA bone density test will report your bone density in numbers. These numbers are sometimes reduced to an overall number -- your T score.  In a DXA test, the amount of mineralized tissue within a section of spine or hip is measured and expressed as grams per cm2.  Values are compared to others of the same age and gender (Z score) or to healthy 35-year-olds of the same gender who are felt to have attained peak bone mass (T score).  These scores are then expressed as measurements of deviation from the average.

So what DXA score means I have osteoporosis?
The World Health Organization (WHO) has established criteria for the diagnosis of osteoporosis:

  • Individuals within one standard deviation of peak bone mass (T score) are considered to have normal bone density.
  • If bone mass is between one and 2.5 standard deviations below peak bone mass (T score), osteopenia is diagnosed.
  • If bone mass is 2.5 standard deviations below peak bone mass (T score), osteoporosis is diagnosed.
  • If the patient has also had a fragility fracture, severe osteoporosis is diagnosed.

What kind of calcium should I take?
The two most available forms of calcium are calcium carbonate and calcium citrate. Either type is an acceptable replacement. Some evidence supports better absorption of calcium citrate. This preparation may be a more judicious choice in patients with achlorhydria or nephrolithiasis. It can be taken with or without meals. Calcium carbonate is better absorbed with meals because it requires an acid stomach for maximal absorption. Read more about recent news concerning calcium supplements and osteoporosis.

When do I need to take medication?
Most authorities, including the National Osteoporosis Foundation, recommend the addition of antiresorptive therapy if the T score is -1.5 SD or greater with major risk factors for fracture, or - 2.0 SD or greater without risk factors. Of course, decisions about treatment must be made based on each individual's bone density and associated medical conditions.

How do drugs for osteoporosis work?
Drugs now prescribed slow bone destruction and resorption. They include:

  • bisphosphonates such as alentronate and risedronate, taken as pills once daily or once weekly, depending on the dose;
  • estrogen replacement for post-menopausal women, taken as pills once daily
  • selective estrogen receptor modulators (SERMs) such as tamoxifen and raloxifene, taken as daily pills.
  • calcitonin, a nasal spray

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