DXA Interpretation — SCE Rheumatology MCQ

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EasyMetabolic Bone DiseaseDXA InterpretationSCE Rheumatology

A 65-year-old postmenopausal woman with no previous fragility fracture undergoes technically valid central DXA. Her T-scores are -1.5 at the L1-L4 lumbar spine, -2.7 at the femoral neck and -2.2 at the total hip. Which principle should be used to assign her densitometric diagnostic category?

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Correct answer: A — Use the lowest valid T-score among the lumbar spine, femoral neck and total hip

The correct answer is A. Clinical densitometric classification uses the lowest technically valid T-score from the accepted central DXA sites: the L1-L4 lumbar spine, femoral neck or total hip. Her femoral-neck T-score of -2.7 therefore places her in the osteoporosis range, despite osteopenic values at the other sites. The measurements are not averaged. The femoral neck is the BMD site entered into FRAX and underpins the WHO epidemiological reference definition, but it is not the only site used in routine clinical DXA classification. Neither the total hip nor lumbar spine automatically takes priority. Apparent spinal elevation from degenerative change should be considered in older patients, although the stem specifies technically valid measurements. Treatment decisions should subsequently incorporate fracture probability and clinical risk factors rather than the T-score category alone.

Reference: Madden K et al. A Statistical Approach Regarding the Diagnosis of Osteoporosis and Osteopenia From DXA: Are We Underdiagnosing Osteoporosis? JBMR Plus. 2021. https://pubmed.ncbi.nlm.nih.gov/26882774/