How does the WHO define osteoporosis?

Updated: Jan 20, 2021
  • Author: Rachel Elizabeth Whitaker Elam, MD, MSc; Chief Editor: Herbert S Diamond, MD  more...
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Bone mineral density (BMD) scores are related to peak bone mass and, subsequently, bone loss. Whereas the T-score is the patient’s bone density compared with the BMD of control subjects who are at their peak BMD, the Z-score reflects a bone density compared with that of patients matched for age and sex. [7, 8, 9, 10]

The World Health Organization’s (WHO) definitions of osteoporosis, which are based on BMD measurements in white women, are summarized in Table 1, below. [9, 10] For each standard deviation (SD) reduction in BMD, the relative fracture risk is increased 1.5-3 times. The WHO definition applies to postmenopausal women and men aged 50 years or older. Although these definitions are necessary to establish the prevalence of osteoporosis, they should not be used as the sole determinant of treatment decisions. This diagnostic classification should not be applied to premenopausal women, men younger than 50 years, or children.

Table 1. WHO Definition of Osteoporosis Based on BMD Measurements by DXA (Open Table in a new window)


Bone Mineral Density Measurement



BMD within 1 SD of the mean bone density for young adult women

T-score ≥ –1

Low bone mass (osteopenia)

BMD 1–2.5 SD below the mean for young adult women

T-score between –1 and –2.5


BMD ≥2.5 SD below the normal mean for young-adult women

T-score ≤ –2.5

Severe or “established” osteoporosis

BMD ≥2.5 SD below the normal mean for young-adult women in a patient who has already experienced ≥1 fracture

T-score ≤ –2.5 (with fragility fracture[s])


(1) World Health Organization (WHO). WHO scientific group on the assessment of osteoporosis at primary health care level: summary meeting report. Available at: Accessed August 21, 2020 [18]

(2) Kanis JA. Assessment of fracture risk and its application to screening for postmenopausal osteoporosis: synopsis of a WHO report. WHO Study Group. Osteoporos Int. Nov 1994;4(6):368-81. [10]

(3) Czerwinski E, Badurski JE, Marcinowska-Suchowierska E, Osieleniec J. Current understanding of osteoporosis according to the position of the World Health Organization (WHO) and International Osteoporosis Foundation. Ortop Traumatol Rehabil. Jul-Aug 2007;9(4):337-56. [9]

BMD = bone mineral density; DXA = dual x-ray absorptiometry; SD = standard deviation; T-score = a measurement expressed in SD units from a given mean that is equal to a patient's BMD measured by DXA minus the value in a young healthy person, divided by the SD measurement in the population.

The WHO recommends incorporating clinical risk factors into decision making about osteoporosis, rather than relying solely on the use of bone mineral measurements. BMD has high specificity but low sensitivity, meaning that the risk of a fracture is high when the BMD indicates that osteoporosis is present, but is by no means negligible when BMD is normal.  [18]

Z-scores should be used in premenopausal women, men younger than 50 years, and children. Z-scores adjusted for ethnicity or race should be used, with Z-scores of –2.0 or lower defined as "below the expected range for age" and with Z-scores above –2.0 being defined as "within the expected range for age." Again, the diagnosis of osteoporosis in these groups should not be based on densitometric criteria alone.

For more information, see the following:

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