Do I Need a Bone Density Test?

A DEXA Scan Bone Density Test Can Tell Your Risk of Osteoporosis

DEXA scan screen
MartinPoulter/Wikimedia Commons/Creative Commons

Bone density testing is recommended to diagnose bone loss and osteoporosis. The most common test is the dual-energy x-ray absorptiometry (DEXA) scan. Osteoporosis causes a decrease in bone mass, often referred to as thinning of bone. When this occurs, the patient with osteoporosis will have weaker bones and have a higher risk of bone fracture.

Who should have a DEXA Bone Density Test?

The National Osteoporosis Foundation has these clinical guidelines.

They recommend a DEXA scan at a facility that uses accepted quality assurance measures.

  • All women age 65 and older and men age 70 and older should be tested.
  • If they have risk factors, postmenopausal women and men age 50-69 should be tested.
  • If you have had an adult age fracture and are a postmenopausal woman or a man of age 50 or older, a bone mineral test can help diagnose the degree of osteoporosis.

The current recommendation from the U.S. Preventative Services Task Force is for a bone density test at least once for all women age 65 and older as well as in younger women whose risk factors raise their fracture risk is equal to or greater than that for a 65-year old white woman who has no additional risk factors. These guidelines are being reviewed and updated.

Risk Factors for Osteoporosis

Some of the common risk factors include:

  • Being female
  • Advanced age
  • Being Caucasian or Asian
  • Low bone mass
  • Being thin or having a small frame
  • A sedentary lifestyle
  • A family history of osteoporosis
  • Estrogen deficiency as a result of menopause, especially early or surgically induced
  • Anorexia nervosa
  • Use of certain medications
  • Cigarette smoking
  • Excessive alcohol intake

What is a DEXA Scan Bone Density Test?

DEXA stands for "dual-energy x-ray absorptiometry," and is considered the most accurate test for bone density.

While standard x-rays show changes in bone density after about 40% of bone loss, a DEXA scan can detect changes after about a 1% change. A DEXA scan lasts about 10 minutes and exposes the patient to less radiation than a standard chest x-ray (about the same amount of radiation exposure as taking a trans-continental flight).

What Do My Bone Density Test Results Mean?

The results of a bone density measurement (DEXA scan) are reported in two ways: as T-scores and as Z-scores.

A T-score compares your bone density to the optimal peak bone density for your gender. It is reported as the number of standard deviations below the average.

  • A T-score of greater than minus-1 is considered normal.
  • A T-score of minus-1 to minus-2.5 is considered osteopenia, and a risk of developing osteoporosis.
  • A T-score of less than minus-2.5 is diagnostic of osteoporosis.

A Z-score is used to compare your results to others of your same age, weight, ethnicity, and gender. This is useful to determine if there is something unusual contributing to your bone loss.

A Z-score of less than minus-1.5 raises a concern that factors other than aging are contributing to osteoporosis. These factors may include thyroid abnormalities, malnutrition, medication interactions, tobacco use, and others.

Does Medicare pay for DEXA Scans?

Current Medicare Part B (Medical Insurance) guidelines cover this test at no cost once every 24 months, or more often if medically necessary. You are eligible in the following cases:

  • You are a woman whose doctor determines you are low on estrogen and at risk for osteoporosis.
  • To assess your response to osteoporosis medications
  • If you have a condition called primary hyperparathyroidism
  • If you have certain spinal abnormalities that might indicate a fracture
  • If you're on long-term corticosteroid therapy, such as prednisone

Pros for Getting a DEXA Scan

  • Tells if you have osteoporosis
  • Helpful predicting risk of broken bones
  • Determines the need for treatment and monitors its effectiveness

Cons for Getting a DEXA Scan

  • Risk of fracture is dependent on more factors than just bone density
  • May encourage patients to take unnecessary medications
  • Exposes patient to low levels of radiation

Sources:

National Osteoporosis Foundation. Clinician's Guide to Prevention and Treatment of Osteoporosis. Washington, DC: National Osteoporosis Foundation; 2013.

U.S. Preventive Services Task Force. Screening for osteoporosis: recommendation statement. Am Fam Physician. 2011;83:1197-200. PMID: 21568254 www.ncbi.nlm.nih.gov/pubmed/21568254.

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