How test results are read
In BMD test results, your bones are compared to the bones of an average young adult. A score (called a T-score) is calculated that describes the density of your bones (usually at the spine and hip) and tells you how strong your bones are compared to this average. While some bone loss with aging is considered normal, making such comparisons helps to determine whether you are losing bone more rapidly than expected for someone your age.
The T-score is expressed in units referred to as “standard deviations (SDs). These SD units tell us how far you differ (or deviate) from what is considered normal for a young adult. “Below normal is always indicated with a minus (-) sign. A T-score below 2.5 SDs indicates osteoporosis and a score between 1 and 2.5 SDs indicates “osteopenia” or low bone density. Normal bone density is no more than 1 SD below the young adult normal value.
Your BMD test result is only part of the picture in determining your risk for fracture. Two 10-year fracture risk assessment tools are now available for Canadians:
In 2005, Osteoporosis Canada, in association with the Canadian Association of Radiologists, launched the 10-year absolute fracture risk assessment – CAROC.
In addition to BMD (lowest T-score of hip and lumbar spine), age, gender, fracture history and steroid use are taken into consideration to determine an individual’s 10-year risk of fracture.
The presence of both a fragility fracture and steroid use puts the patient at high fracture risk regardless of BMD result.
Version 2, now available for Canadian physicians, uses only femoral neck (hip) BMD rather than the lowest of hip and lumbar spine.
In addition to femoral neck (hip) BMD, age, gender, fracture history and steroid use, FRAX also takes into account other clinical risk factors to calculate the absolute 10-year risk of a hip fracture or other major osteoporotic fracture (spine, forearm, upper arm). These factors include:
- BMI (weight to height ratio calculation)
- Parental hip fracture
- Rheumatoid arthritis
- Other secondary conditions that contribute to bone loss
- Current smoking
- Alcohol intake (three or more drinks per day)
The FRAX system is based upon a more complete set of clinical risk factors and it can be used without BMD results; but it requires access to FRAX software, website or paper chart.
CAROC is less complete but captures the major risk factors for fracture and is easy to use.
For the majority of people, the results are the same regardless of which of these tools is used. Therefore the choice of FRAX or CAROC by the clinician is a matter of personal preference and convenience.