A patient with osteopenia diagnosis per T-score of -3 in a distribution where 68% falls between -1.5 and 1.5:

In this distribution, 68% between -1.5 and 1.5 means 1 SD = 1.5. A T-score of -3 = -2 SD from the mean (0). Osteopenia is diagnosed at >1 SD below peak density (T-score u2264 -1.5 in this scale); osteoporosis at u22652.5 SD below (-3.75 in this scale). T = -3 satisfies osteopenia but not osteoporosis.