Bone Density T-score Explainer

Type the numbers from your DXA report. You get the WHO category for each site, which score applies to you (T or Z), and what the number means for fracture risk, in plain words.

The WHO thresholds

T-score	Category	Examples (BHOF)
−1.0 or higher	Normal	0.9, 0, −0.9
Between −1.0 and −2.5	Low bone mass (osteopenia)	−1.1, −1.6, −2.4
−2.5 or lower	Osteoporosis	−2.6, −3.3, −3.9

For women before menopause and men under 50, ISCD prefers Z-scores: −2.0 or lower is "below the expected range for age", above −2.0 is "within the expected range".

What to do with the number

A T-score is one input. Treatment decisions usually also weigh a 10-year fracture probability from FRAX, which adds age, prior fractures, steroids, smoking and more. Calcium and vitamin D are the base layer everyone gets asked about. Check your daily calcium with the calcium intake checker; the target rises to 1,200 mg for women over 50.

Common questions

What T-score means osteoporosis?

−2.5 or lower. The WHO classification, used for postmenopausal women and men 50 and over: −1.0 or higher is normal, between −1.0 and −2.5 is low bone mass (osteopenia), and −2.5 or lower is osteoporosis.

What's the difference between a T-score and a Z-score?

A T-score compares your bone density with a healthy young adult; a Z-score compares it with people your age. ISCD prefers Z-scores before menopause and in men under 50: −2.0 or lower is 'below the expected range for age'.

How much does each point matter?

NIAMS says fracture risk rises 1.5 to 2 times with each 1-point drop in T-score.

Which site counts?

ISCD: osteoporosis can be diagnosed in postmenopausal women and men 50+ if the T-score at the lumbar spine, total hip or femoral neck is −2.5 or less. Your report usually lists each site; the lowest one drives the category.

How it's computed

For postmenopausal women and men 50+, each entered T-score is classed by the WHO cut-offs (≥ −1.0 normal, > −2.5 to < −1.0 low bone mass, ≤ −2.5 osteoporosis); the lowest of spine, total hip and femoral neck sets the overall category, as ISCD describes. For women before menopause and men under 50 the Z-score is used (≤ −2.0 below expected range for age) and T-scores are shown for reference only. The risk line restates the NIAMS figure (1.5–2× per point); it is not a personal fracture probability. Not a diagnosis.

Sources

WHO Study Group. Assessment of fracture risk and its application to screening for postmenopausal osteoporosis. WHO Tech Rep Ser. 1994;843:1-129. pubmed.ncbi.nlm.nih.gov
International Society for Clinical Densitometry. 2023 Official Positions — Adult. iscd.org
NIAMS (NIH). Bone Mineral Density Tests: What the Numbers Mean. www.niams.nih.gov
Bone Health & Osteoporosis Foundation. Bone density exam/testing. www.bonehealthandosteoporosis.org
FRAX fracture risk assessment tool. www.fraxplus.org