Bone Density Test (Dexa Scan)

Bone density tests are performed to diagnose osteoporosis; estimate bone loss and efficacy of osteoporosis medications, and to predict the risk of a future fracture. This test is recommended for women beyond the age of 65 years. Men are recommended to undergo testing after the age of 70 years. Young women and men of any age must undergo bone density test if they show risk factors, such as:

• Possibility of fractures after the age of 50 years
• Family history of osteoporosis
• History of prostate cancer or breast cancer
• History of rheumatoid arthritis, thyroid disorders and anorexia nervosa
• Early menopause
• Long-term use of corticosteroids or thyroid hormone
• Low body weight
• Significantly short height
• Long-term use of tobacco or alcohol (Read more: Effects of alcohol on body)

All calcium supplements should be discontinued for at least 24 hours prior to the test. If the person has undergone any procedure involving the intake of a contrast dye for barium studies, computed tomography or magnetic resonance imaging scan, he/she should wait for at least a week as the dye can interfere with results. All metal belts and buttons must be removed before the test.

This test can be performed in two ways. The most common and accurate method is a DEXA scan in which a low dose of X-ray radiation is used. There are 2 types of DEXA scans:

• Central DEXA: In this procedure, the person lies on a table and the scanner is passed over the lower lumbar region and spine. Undressing is not required in most cases. No zippers should be included in the scan. This method can best predict the risk of hip fractures.
• Peripheral DEXA: Smaller machines are used to measure bone density in wrist, fingers, leg and heels. Such machines are often seen in healthcare offices, medical camps, etc.

Both procedures are painless. The person only needs to remain still during the test.

Normal results: Two scores are received after the test: T score and Z score. T score compares the bone density with another healthy young adult of the same gender as the patient who undergoes the test.

• T score of -1 and above: Indicates normal  bone density
• T score of -1 to -2.5: Indicates low bone density and risk of osteoporosis
• T score of -2.5 and above: Indicates osteoporosis

Z score compares the bone mass of other people of the same age, gender and size. A Z score below -2.0 indicates low bone mass caused due to factors other than ageing and requires additional investigations.

Abnormal results: An abnormal DEXA test does not help in detecting fractures. Along with pre-existing risk factors, it only predicts the risk of a fracture in the future. An abnormal DEXA scan may also be seen in the presence of other risk factors, such as:

• Rheumatoid arthritis
• Inflammatory bowel disease
• Chronic liver and renal failure
• Respiratory diseases

While repeating the DEXA scan, it is recommended to perform the test at the same place. This helps in accurate comparison with previous reports. Even if it may not always be possible to undergo the test at the same place, it is necessary to compare the density scores. X-rays cannot replace bone density tests, because they cannot show osteoporosis until the disease is at an advanced stage. However, X-rays can be recommended along with a bone density scan to detect fractures in other parts of the body.

Disclaimer: All results must be clinically correlated with the patient’s complaints to make a complete and accurate diagnosis. This information is purely from an educational perspective and is in no way a substitute for medical advice from a qualified doctor.