A Z-score provides bone density information relative to age-matched peers, while a T-score compares to a younger, healthier reference group.

“So when you're looking at your BMD, it's going to give you a Z-score. So a Z-score of zero means, and you understand this, but it's like, a Z-score referring to a probability distribution in a standard mode. So Z-score of zero means you're at the 50th percentile for your age and sex. A Z-score of plus one, you're one standard deviation above, minus one, below, et cetera. There's also a T-score, which is doing the same thing, but comparing you to a young person. And so the T-score is technically used to make the diagnosis of osteopenia or osteoporosis. We tend to look more at the Z-score, and basically say, look, if your Z-score right now is minus one, in four years I want your Z-score to be zero.”