How Should GPs Use Bone Densitometry?

Selecting Patients for DXA Scan

BMD, a prior fracture and age are the most powerful contributors to future fracture risk. Consider a scan in any patient at risk of osteoporosis in whom knowledge of BMD may influence management. Your local DXA service is likely to have locally agreed referral criteria to follow and there is also advice from bodies such as NICE (primary and secondary fracture prevention in postmenopausal women), SIGN (management of osteoporosis) and the Royal College of Physicians (corticosteroid guidance). More information about the national guidance available is given in the Initiation section.

It may be helpful to use the FRAX(r) tool to estimate the patient's 10-year fracture probability and the associated NOGG guidance to decide whether DXA referral would be helpful. Even if the fracture risk is very high and the patient definitely requires treatment, it still may be helpful to know their BMD in order to assess the severity of their osteoporosis and as a baseline to monitor their progress.

In many cases, it is clinically appropriate and feasible to send a patient over the age of 75 for a DXA scan, although NICE guidance allows for a diagnosis to be assumed in this age group where this is not the case.

When referring a patient for a DXA scan, the National Osteoporosis Society leaflet Scans and Tests may be helpful.

Repeating DXA Scans in Patients at Risk of Osteoporosis

Most DXA services provide information about the interpretation of the BMD result for an individual patient. If this is not available, it is important to remember that there are other risk factors for fracture that should also be taken into account when interpreting the BMD result. BMD of the femoral neck can be entered into the FRAX(r) probability assessment for a patient who has not already been treated for osteoporosis.

Good practice for reporting DXA scans is outlined in the National Osteoporosis Society Practical Guide Reporting Dual Energy Absorbtiometry Scans in Adult Fracture Risk Assessment.

Repeating DXA Scans in Patients at Risk of Osteoporosis

The decision as to whether and when to repeat a DXA scan will depend on the initial results and the individual patient's circumstances. Factors to take into account are whether the patient has risk factors for accelerated bone loss, such as corticosteroid therapy, medical conditions or treatment predisposing the patient to bone loss, such as inflammatory disease, malabsorption, aromatase inhibitor therapy or recent menopause. It is rarely helpful to repeat DXA scans within 2 years. Repeat measurements should be guided by local service agreements and the advice given at the time of the baseline scan.

Using Follow-up Scans to Monitor Treatment

There is a lack of consensus on this issue. DXA scans are of limited value in assessing response to treatment and a treatment response can rarely be demonstrated in less than 2 years. This is because the changes in BMD in response to treatment are small and slow and similar in magnitude to the error of the DXA measurement. However, repeat measurement of BMD can provide positive reinforcement to encourage continued compliance with treatment and is helpful in identifying patients who are not responding adequately to treatment.