Normal Bone Density- Your bone density is within the healthy range, and you have a low risk of fractures under normal bone stress.
Osteopenia- Your bone density is below the normal range, but not low enough to be diagnosed as osteoporosis. You also have a slightly higher risk of fracture. While osteopenia is not as bad as osteoporosis, if it is ignored, the bones could continue to lose bone density and become osteoporotic. Treatment is often appropriate at this stage.
Osteoporosis- Your bone density is significantly lower than the normal healthy range and your risk of fracture is significantly higher than people in the normal range.
Severe Osteoporosis- You have osteoporosis and you've had at least one "fragility" fracture.