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From the Research
T Scores and Z Scores in DXA Measurements
- T scores and Z scores are used to present the results of bone mass measurements in dual-energy X-ray absorptiometry (DXA) 1.
- T scores compare an individual's bone mineral density (BMD) to the mean value of a young healthy reference population, while Z scores compare an individual's BMD to the mean value expected for their age and sex 1.
Age and T Scores and Z Scores
- Studies have shown that T scores and Z scores can differ substantially in young adults [(2,3)].
- The difference between T scores and Z scores can be significant, with up to 11% of cases showing a difference of 1 or more standard deviations 2.
- The smallest differences between T scores and Z scores are seen at the total hip, while the largest differences are seen at the femoral neck 2.
Height Adjustment and T Scores and Z Scores
- Height adjustment is important when assessing DXA measurements of bone mass and density in children 4.
- Different methods of height adjustment can result in biased measurements, with adjustments using height-for-age Z-scores being the least biased 4.
Identical T Scores and Z Scores
- There is no specific age at which T scores and Z scores are identical in DXA measurements, as the difference between the two scores can vary depending on the individual and the skeletal site being measured [(2,3)].
- However, it is expected that T scores and Z scores will be similar in young men and women, as the reference population for T scores is typically a young healthy population 1.