peripheral X-ray absorptiometry is principally used sites such as the forearm, heel and hand
use of peripheral bone mineral density (BMD) measurements to diagnose osteoporosis and make decisions about patient treatment in a 'stand alone' capacity without the ability to refer patients for a hip and spine BMD examination is complicated by:
poor correlation of peripheral measurements with hip and spine BMD
different age dependence of T-scores at different skeletal sites
lack of evidence to show that fracture prevention therapy is effective in patients treated on the basis of a peripheral measurement
recommended that in centres where peripheral BMD measurements are used for performing clinical examinations they are interpreted using a triage approach (1)
in this approach, device-specific upper and lower thresholds are chosen to have 90% sensitivity and 90% specificity for identifying patients with osteoporosis at the hip or spine. This means that 90% of patients who have a T-score of -2.5 or below at either the hip or spine have a peripheral measurement below the upper threshold, and 90% of patients who have T-scores of greater than -2.5 at both central sites have a peripheral measurement above the lower threshold. Based on these thresholds, therapeutic intervention is recommended as follows:
if the peripheral measurement is below the lower threshold, treatment is recommended, especially if other major risk factors for osteoporosis and/or fractures are present
if the peripheral measurement lies between the upper and lower thresholds, hip and spine BMD measurements should be performed to obtain a definitive assessment
if the peripheral measurement is above the upper threshold, and no low trauma fracture is present, no further treatment is required and the patient should be reassured that their risk of fracture is low. In practice it will be necessary for approximately 40% of patients to be referred for BMD measurements of the hip and spine
"...In practice it will be necessary for approximately 40% of patients to be referred for BMD measurements of the hip and spine..."(1)
SIGN state (2):
peripheral DXA predicts the risk of non-vertebral fractures but is less predictive than hip BMD for the prediction of hip fracture and spine BMD for the prediction of spine fracture
(1) National Osteoporosis Society (2011). Peripheral X-ray absorptiometry in the management of osteoporosis.
(2)SIGN (June 2020). Management of osteoporosis and the prevention of fragility fractures.