It is very important that if you are treating patients with bone loss, that you know how to interpret a DXA scan report. The entire DXA report should be looked at, including the graphs and images, not just the total results. A detailed questionnaire should be filled in by the patient to help determine the cause/s of their bone loss, and what is the most suitable medication for that patient. The only test that the Irish Osteoporosis Society (IOS) recommends for the screening and diagnosis of Osteoporosis, is a DXA of the spine and hips. The IOS does not recommend the use of ultra sound scanning of the heel or tibia. The IOS does not recommend FRAX, for risk of fracture, as there are only 12 risk factors on it and there are 200 causes of bone loss.
A T-score compares an adult’s results with the mean peak bone mass of a large number of normal females and males between the ages of 20-40. A Z score compares the patient’s score with their own age group; this is usually used in the diagnosis of the spine in children and adolescents. Their bone age should also be compared to their chronological age, by x –raying the carpal bones of their non-dominant hand.
NOTE: T scores and Z scores are the same between 20 and 40 years.
The Osteopenia range is a T score between -1 and -2.49. It is easier for patients to understand the degree of osteopenia and their risk of fracture. Research shows that the majority of fractures happen in the moderate to marked Osteopenia range.
Mild Osteopenia T-score = -1 to -1.49
Moderate Osteopenia T-score = -1.5 to -1.9
Marked Osteopenia T-score = -2 to -2.49
Osteoporosis T-score = Greater than -2.5
Severe Osteoporosis = -3 or higher
A fragility fracture should be considered Osteoporosis unless proved otherwise, even when the patient has fallen on ice or cement. All individual vertebrae levels should be looked at, as well as both hip areas. If a T score is more than -1 (Better) below the lowest T score, it should be eliminated and not included in the average. A diagnosis should not be made, just on the total average of either the spine or the hip.
If a person has developed a Dowagers hump, loss of height, postural changes: rounded shoulders or head protruding forward from their body, or mid or upper back pain, an LVA (Lateral Vertebral Assessment) of the thoracic spine is recommended if available. An LVA is usually not done unless specifically requested on the referral form. If LVA is not available, a lateral x-ray of the spine is advised. This will show if the shape of the bones in this area are compressed, due to Osteoporosis fractures. However this cannot be used to monitor the patients response to treatment.
NOTE: Many people have arthritis and Osteophytes which will give a false higher bone density reading. A DXA scan usually measures the lumbar spine (L1, L2, L3 and L4) and one or two hips: neck of femur and total hip. The preference is for both hips , as there can be a discrepancy between either side.
Example of DXA results:
T score of L1 = -3.2 = Severe Osteoporosis
T score of L2 = -3.3= Severe Osteoporosis
T score of (L3) = -1.9 = Moderate Osteopenia
T score of (L4) = -2.0= Marked Osteopenia
The average of the above T scores above, prior to elimination = -2.6
L3 and L4 should be eliminated, unfortunately this is not always done. Therefore, after eliminating them, the average T score = -3.25
They are eliminated due to false higher readings, usually due to Osteoarthritis or a fracture. Example: -3.2 is the lowest score, therefore any T score below -2.3 should be eliminated. The patient above should have an LVA done.
Non Dominant Forearm
If only one vertebra is left, because the other vertebrae have been eliminated or both hips have been excluded because of hip replacements, then a DXA on the non-dominate forearm should be done.
Tip: High -T scores of the radius (Ultra Distal, 33% of distal radius and total ) may indicate High Parathyroid levels.
Z scores are used in the results of an LVA. LVA measures the shape of the vertebrae. A Z score of more than -3 score, denotes either a wedge or biconcave fracture. Usually if there are fractures, they are marked with a red flag on the image.
Repeat DXA scanning
Repeat DXA scanning should be done in order to monitor the patients response to treatment. If the patients results have declined, the patient may not have taken the medication, if it is an oral medication, they may not have taken it correctly or may not be absorbing it. They may have developed new risk factors, e.g. an illness or been prescribed medication that causes bone loss. A DXA should be performed if patients are on medication, every two years to encourage compliance and monitor progress. A percentage of patients can reverse their bone density back to normal, this is also another reason why rescanning is important. It is essential that repeat DXA’s are done on the same machine and site for comparison, and that DXA operator and the person reading the scan has done the ISCD course.