A T-score of -1 and above indicates normal bone density for people of all ages when compared to a normal young adult, according to the National Osteoporosis Foundation. Z-scores provide results compared to a similar age and body type as an individual and are not recommended for older people.
T-scores measure how different a person's bone density is from that of a healthy 30-year old adult, the National Osteoporosis Foundation states. A T-score between -1 and -2.5 indicates low bone density, and a score of -2.5 and below means the person has osteoporosis. Z-scores are considered misleading for older individuals because more older people have low bone density.