Barbells4Bones: Understanding Your T-Score
Updated: Sep 23, 2022
Bone scans after menopause are a rite of passage for many women and can turn into an annual affair depending on your individual risk factors including your medication and medical history, fracture history, falls risk, and even your parent's medical history. Despite the looming threat of osteoporosis and osteopenia and the annual trip to the DXA machine, many women are left with lots of fear of fracture and little understanding of what those numbers actually mean. Let's clear that up and help you understand exactly what you're reading when you get back your report.
First, let's understand a few important terms:
Bone Density Test (DXA Scan): A specialized x-ray used to measure the amount of calcium and other minerals in your bone - the higher the density the better! Typically, results are reported as "t-scores" at several important anatomical points, such as the neck of the femur (at the hip) and the lumbar spine (lower back). Those areas are most important because of the severe impact of fractures at those sites, and they're also predictive of bone density elsewhere in the body.
Osteopenia: Literally translated as "thin bones," osteopenia is the diagnosis for someone who has bone density that is lower than normal.
Osteoporosis: The more severe sister of osteopenia, osteoporosis is the diagnosis for someone who's bone density is significantly lower than normal and carries a high risk of osteoporotic or atraumatic fracture.
Osteoarthritis: Has nothing to do with bone density, though it is often confused with osteoporosis. Osteoarthritis refers to highly normal age-related changes to joint surfaces, and we're going to touch on this (and it's myths!) in another post.
What Is A T-Score
A t-score, for anyone that's taken a statistics course, essentially refers to where a data point falls along a normal distribution (or bell curve). T-scores refer to how many standard deviations a point is above or below the average (which is called 0). Rather than being a measurement of "your bone has 85% of its previous strength," t-scores are a ranked comparison of where you are compared to a healthy young adult of the same sex, which can make it confusing to understand.
To make things easier, here is what a normal distribution looks like:
In the middle of the curve is the 50th percentile or the t-score of 0. A person with a t-score of 0 is someone who has bone density that is the same as a healthy young adult of the same sex, which is incredibly impressive!
If we look to the left of 0, we have -1, -2, and -3, respectively. This is where we will find t-scores that are lower than the average healthy young adult, the greater the number, the lower the score. You can also see percentile rankings, so a t-score of -1 means that your bone density is in the 15th percentile for bone density of healthy young adults (ie. less dense than 85% of that population).
Now, before you start panicking that your bones are less dense than 85% of young adults, remember that this is normal and expected. Peak bone density happens around age 30 and decreases every year following, so the farther removed you are from age 30, the more 30-year-olds are going to have higher bone density than you do. That also means that the greater your bone density is earlier in life, the more you have to lose in the long term, leaving you with measurably higher bone density than your peers later in life. In short: pick up heavy things early and often!
When it comes to actually understanding what your t-score means we use ranges to determine the severity of bone density loss:
T-score of 0 to -1: Your bone density is considered normal, congratulations!
T-score of -1 to -2.5: Your bone density is below normal, which indicates osteopenia.
T-score less than -2.5: Your bone density is very low, which indicates osteoporosis
Now that you understand t-scores, let's translate the report that you get from the doctor:
Reading Your Report
If you're lucky enough to get a copy of the report for your bone density scan, it likely won't make a ton of sense, don't panic, we're going to translate the common things you'll see.
In this section, you'll likely have three different t-scores reported, the lumbar spine, the femoral neck, and the total hip. You can apply the ranges we talked about above to understand which areas are at the greatest risk. These numbers together go into determining the next section:
This is the summary of whether your bone density is normal, osteopenic, or osteoporotic based on your t-scores.
BMD Risk Assessment
Most reports will also include a fracture risk assessment which basically gives the estimated risk of a fracture over a 10-year period. Anything over a 20% chance is considered high. This would mean that, based on your age, t-score, fracture history, and some other medical factors, the likelihood of you having a significant fracture in the next 10 years is 1 in 5. Now, if your report doesn't have this information, or if it isn't clear, check out the FRAX tool online that will show you your estimated risk.
This section of your report shows the percentage change in your bone density at all the sites that were assessed (hips and back) relative to your last test and will tell you if it's statistically significant or not. This can also show if your density is decreasing, or if it is maintaining or increasing due to medication, supplementation, or exercise that you've started in order to manage your bone density.
Often, these reports include a section on recommendations for management, whether that is with supplementation, medication, or just lifestyle changes to help manage and improve bone density.
Check back in with this blog while we cover several more topics related to bone density and its management over the next few weeks!
Clare Donaldson is a Registered Physiotherapist, new mom, Crossfit enthusiast, poor but passionate hockey player, and genuine lover of all things physiotherapy. She is especially interested in keeping moms of all ages strong and healthy throughout their lives. When she's not at CONNECT, you can find Clare hiking with her dog, Moose, or spending time with her young family. To find Clare at CONNECT, click here