T-score and Z-score in osteoporosis

Point

T-score

Z-score

Number of SD a patient’s

BMD is above or below the

mean for healthy young adult

reference population

Number of SD a patient’s

BMD is above or below the 

mean for age, sex, and

ethnicity-matched population

Reference

group

Healthy young adults

(typically 20–30 years old)

People of the same 

age, sex, race

Use

To diagnose osteoporosis

To check if bone loss is

unusual for age

(secondary causes)

WHO

Criteria

• Normal: T ≥ –1

• Osteopenia: –1 to –2.5

• Osteoporosis: ≤ –2.5

No fixed cut-off

Z ≤ –2: “below expected for age”

Applies to

• Postmenopausal women

• Men ≥50 yrs

• Premenopausal women

• Men <50 yrs

• Children