How Diagnosis of Osteoporosis Is Done
The gold standard for diagnosis of osteoporosis is dual energy x-ray absorption scan (DEXA scan). The test is performed by passing low energy x-rays through a bone (e.g. spine, hip or wrist). The test takes about ten minutes, is painless, and is associated with very limited radiation exposure. The values generated by the test can then be compared to both:

• Young adult population—called a "T score", this test measures the variance between the patient and the young adult baseline. A score above -1 is considered normal; a score between -1 and -2.5 is considered osteopenia; and a score below -2.5 is considered osteoporosis. For each -1 standard deviation in T score there is a 3 times increased risk of hip fracture and a 2.5 times risk of spine fracture.

• Age- and gender-matched control groups—a "Z score" measures the variance between the patient’s and control groups’ amount of bone. The control group consists of other people in the patient’s age group of the same size and gender. An unusually high or low score may indicate the need for additional tests.

Using statistical analysis, the DEXA scan diagnostic study can indicate if someone is at increased risk of sustaining a fracture. According to the National Osteoporosis Foundation, bone mineral density testing is recommended in the following situations:

• All women over age 65

• Postmenopausal women under age 65 who have multiple risk factors

• At menopause, if undecided about hormone replacement therapy

• Abnormal spine x-rays

• Long-term oral steroid use

• Hyperparathyroidism (over-active parathyroid gland)

An osteoporosis diagnosis distinguishes whether or not osteoporosis is a primary problem or is secondary to another problem. Therefore, a thorough history and physical examination, as well as the appropriate diagnostic tests, need to be obtained. It is important to distinguish primary from secondary because the treatments are often different.

Common causes of secondary osteoporosis include:

• Endocrine disorders (hypogonadism, Cushings disease, hyperthyroidism, hyperparathyroidism, diabetes mellitus)

• Marrow disorders (multiple myeloma, disseminated cancer, chronic alcohol use, lymphoma)

• Collagen disorders (osteogenesis imperfecta, Marfans syndrome)

• Gastrointestinal disorders (Malabsorption, malnutrition)

• Medications (Aluminum antacids, anti-convulsants, chemotherapy, glucocorticoid therapy, thyroid hormone replacement)

By: Donald J. Frisco, MD
June 21, 2006 (Originally published November 1999)