Osteopenia and osteoporosis are related. They both involve the loss of minerals from the bones. Osteopenia is the loss of a measurable amount of bone. Osteopenia can progress to osteoporisis. In osteoporosis, the bones have lost so much material that they have become porous.
When you have your bone mineral density tested, the results are described by a T score. A T score compares your bone density to the average bone density of a healthy person of your same age and gender. A positive score means that your bones are denser than the average healthy person. A negative score means you have less bone density than average. If your T score is between -1 and -2.5, you are classified as having osteopenia. If your score is -2.5 or lower, you have osteoporosis.