This 1994 WHO-affiliated perspective by Kanis et al. asked how to convert the continuous relationship between BMD and fracture risk into clinically actionable diagnostic categories. It proposed the T-score framework — referenced to the young adult mean — defining Normal, Osteopenia, Osteoporosis, and Severe Osteoporosis. The paper also explains why age-matched Z-scores are inadequate as diagnostic tools.
Every time you read a DEXA report, you are using the framework this paper created. Before 1994, there was no standardized definition — clinicians used fracture thresholds set at arbitrary points, and age-matched Z-scores were common, masking the true rise in fracture risk with aging.
The practical rule: use T-scores (young adult reference), not Z-scores, for diagnosing osteoporosis in postmenopausal women. A T-score below −2.5 SD meets the threshold. A fragility fracture on top of that defines severe (established) osteoporosis and should prompt immediate treatment evaluation.
Remember the gradient: each 1 SD drop in BMD roughly doubles fracture risk. A patient at −2 SD does not just have "low bone density". She carries approximately four times the hip fracture risk of a woman at average BMD.
The −2.5 SD cutoff is pragmatic, not biological. The authors explicitly acknowledged it would evolve. It has. FRAX (Kanis et al., 2008) built directly on this framework, incorporating clinical risk factors alongside BMD to refine individual fracture probability.
This 1994 WHO-affiliated perspective by Kanis et al. asked how to convert the continuous relationship between BMD and fracture risk into clinically actionable diagnostic categories. It proposed the T-score framework — referenced to the young adult mean — defining Normal, Osteopenia, Osteoporosis, and Severe Osteoporosis. The paper also explains why age-matched Z-scores are inadequate as diagnostic tools.
Every time you read a DEXA report, you are using the framework this paper created. Before 1994, there was no standardized definition — clinicians used fracture thresholds set at arbitrary points, and age-matched Z-scores were common, masking the true rise in fracture risk with aging.
The practical rule: use T-scores (young adult reference), not Z-scores, for diagnosing osteoporosis in postmenopausal women. A T-score below −2.5 SD meets the threshold. A fragility fracture on top of that defines severe (established) osteoporosis and should prompt immediate treatment evaluation.
Remember the gradient: each 1 SD drop in BMD roughly doubles fracture risk. A patient at −2 SD does not just have "low bone density". She carries approximately four times the hip fracture risk of a woman at average BMD.
The −2.5 SD cutoff is pragmatic, not biological. The authors explicitly acknowledged it would evolve. It has. FRAX (Kanis et al., 2008) built directly on this framework, incorporating clinical risk factors alongside BMD to refine individual fracture probability.