The 29-Year-Old Who Wants a DXA
A 29-year-old woman requests bone density testing. She has a history of anorexia nervosa since age 17, BMI 16.8, and secondary amenorrhea for 4 years. She has had two low-trauma metatarsal stress fractures in the past 18 months. She is otherwise healthy, on no medications except a combined oral contraceptive that her gynecologist started 'for bone protection.' The technologist asks you whether to scan her, and if so, how to interpret the result, since the manufacturer's reference database stops at age 20 and the printed report will show a T-score.
1. Should she be scanned, and which reporting parameter applies?
Read the worked answer
Yes, scan her. ISCD indications include estrogen deficiency and a condition associated with low bone mass or bone loss; anorexia nervosa with prolonged amenorrhea and fragility-type fractures is a clear indication, and age alone is not a contraindication when there is a strong clinical reason.
The reporting parameter, however, is Z-score, not T-score. T-scores are reserved for postmenopausal women and men ≥50 for diagnostic classification against the young-adult reference. In a premenopausal woman under 50, the appropriate comparison is age-matched: report the Z-score and interpret it as 'below the expected range for age' if ≤ −2.0. A printed T-score may appear on the manufacturer output; it should not be used to assign a diagnosis of osteoporosis in this patient.
This is a classic exam trap: the machine will happily print a T-score, and the report will look authoritative. The interpreter must override it.
2. The scan returns lumbar spine Z-score −2.6, femoral neck Z-score −2.1. How do you phrase the diagnosis and what do you tell her about the oral contraceptive?
Read the worked answer
Diagnosis phrasing: 'Bone mineral density is below the expected range for age' at the spine (Z −2.6) and femoral neck (Z −2.1). Do not write 'osteoporosis' - that term in a premenopausal woman requires a fragility fracture plus low bone mass, and even then is used cautiously; the Z-score terminology is the ISCD-consistent language. Note the two metatarsal stress fractures as fragility-type fractures in a young woman with anorexia.
Oral contraceptive: combined estrogen-progestin pills are not an established bone-protective therapy, and in a young woman with hypothalamic amenorrhea from energy deficiency, the primary driver is low energy availability, not estrogen deficiency per se. The evidence does not support COCs as a treatment for low BMD in anorexia; the priority is nutritional rehabilitation and weight restoration, with bone health as a secondary outcome. Saying this diplomatically to the patient (and to the gynecologist) is part of the job.
Also worth flagging: repeat DXA should not be done sooner than ~1–2 years unless there is a clinical reason, and the same scanner/software should be used for comparison.