A 32-year-old woman with anorexia nervosa and amenorrhoea undergoes DXA scanning. Her lumbar spine result is reported as a Z-score of -2.4. How should this result be interpreted?
- A Osteoporosis, because a Z-score below -2.5 defines it
- B Normal, because Z-score is not valid before menopause
- C Low bone density below the expected range for her age ✓
- D Osteopenia, because the score lies between -1.0 and -2.5
Correct answer: C. Low bone density below the expected range for her age
Explanation
In premenopausal women, premenopausal men and children, the Z-score (comparison with age-matched controls), not the T-score, is used. A Z-score at or below -2.0 defines 'low bone density below the expected range for age'. The T-score thresholds (-1.0 and -2.5) apply only to postmenopausal women and men above 50 years. Option D wrongly applies T-score cutoffs, and option A invents a Z-score threshold that does not exist.
Reference: Harrison's Principles of Internal Medicine, 21st ed.
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