I recently received a question: why is my T score going up and my fragility score getting worse? This is a great question. Let's take this step by step.
First let's address the T-score. When tracking bone health over time, we must evaluate the actual numbers for Bone Mineral Density (BMD), not T-score. The T-score is a nice way to get an overall picture of your BMD compared to a 30-year-old white female. It is easy to get sucked into comparing T-scores, as we have all been conditioned to look at T-scores. However, T-scores represent standard deviations on a graph, and they represent a range of numbers and not absolute values of BMD. Therefore, tracking bone density over time can only be done by comparing BMD values in g/cm2 and expressing those changes as percentages compared to baseline and compared to the result immediately prior.
There are several factors that cause the BMD and therefore T-scores to change including age, levels of activity, nutrition and build. In post-menopausal women, there is a natural reduction of BMD and T scores over time which can be slowed, and in some cases reversed, with attention to good nutritional balance and lots of impact and resistance exercise. These changes usually occur slowly and are often not detectable on DXA scans in under several years because the Least Significant Change (LSC) is 5-6% which is not sensitive enough to measure a few percentage points difference. REMS can detect such changes, usually at yearly intervals. Changes in BMD caused by increases or decreases in weight and thus Body Mass Index (BMI) occur more quickly, and these changes can often be detected by REMS over a period of months rather than years. If the change is sufficiently large, DXA will be able to detect it in similar timeframes.
For simplicity, let’s say BMD in 2022 was 0.983 g/cm2. Then in 2024, BMD was 0.899 g/cm2.
The change in BMD is calculated as follows:
0.899 - 0.983 = -0.084 This demonstrates a decrease BMD (g/cm2) over 2 years.
To find the percent change, divide -0.084 by the original BMD (g/cm2)
-0.084 ÷ 0.983 = -0.085 This indicates there was an 8.5% decrease in BMD (g/cm2).
Remember to take into consideration the LSC which are different for DXA and REMS. A generally accepted LSC for DXA is 5-6%. So, if the change in BMD over time is less than 5-6%, it is not necessarily a real change when measure by DXA. If the change is greater than 5-6%, it does represent a real change. LSC for REMS is 0.88-1.05% (0.88% for hip and 1.05% for spine) meaning it can detect smaller changes, often in shorter timeframes. In the example provided above, there was a real change in BMD, as 8.5% is greater than 5-6% for DXA and 0.88-1.05% for REMS.
Fragility Score is an adimensional number from 0-100. The lower the score, the better. FS reflects the micro-architecture of the bone. The AI in REMS technology compares the acquired spectra from the patient to a reference database. If the patient’s spectra match the spectra of individuals who have fractured, the patient will be in the RED. If the patient’s spectra match the spectra of individuals in the database who did not fracture, then the patient will be in the GREEN. YELLOW indicates some individuals fracture, and some did not.
There is a natural increase in FS over time which is in the range of 1.5 – 2.0% per year in post-menopausal women. If the difference in FS over, for instance three years, is 4-5, that change may be inconsequential, considering the LSC and the expected change with age.
Remember, you are more than your T-scores or Z-scores. Knowledge brings empowerment and peace of mind.