Note: These guidelines are evidence-informed and are based on expert opinion or case studies. They should not diminish the freedom of practitioners to determine and order imaging studies for their patients.
BMD REFERENCE INFORMATION AND DEFINITIONS
T-score: number of standard deviations above (+) or below (-) mean peak young adult bone density. Used for individuals >50y age.
Z-score: number of standard deviations above (+) or below (-) the mean density for an individual of same age and sex. Used for individuals <50y age CAROC 2013 revision.
LSC: Least Significant Change: amount by which one BMD value must differ from another for the difference to be statistically significant to 95% level of confidence. This corresponds to 2.77 times the precision error for single measurements at each time point for 95% certainty.
Mayfair BMD technologist-specific precision error is 0.010 g/cm2 with LSC considered to be 0.028 g/cm2 for 95% certainty. When there is less bone density, there is less precision.
*** IMPORTANT *** NEW RECOMMENDED DIAGNOSTIC CATEGORIESCAROC 2013 REVISED ***:
For women and men =>50y : NORMAL (T-score greater than or equal to -1.0), LOW BONE MASS (previously OSTEOPENIA) (T-score -1.1 to -2.4), and OSTEOPOROSIS (T-score less than or equal to -2.5).
For women and men < 50y and children <18y, the diagnosis of osteoporosis should not be made on the basis of BMD alone. In these age groups, Z-score above or below -2.0 is used to categorize density WITHIN EXPECTED RANGE FOR AGE (Z-score greater than -2.0) or density BELOW EXPECTED RANGE FOR AGE (Z-score less than or equal to -2.0).
*** Also under the current revised guidelines, Z score now reported for individuals under age 50 with PREVIOUS guidelines using T-score for femur and spine areas in this age group (unless pediatric). A change in Z score compare to prior T score when comparing to past examination may not indicate a significant change in density. Instead refer to specific category and density change comments.
*** IMPORTANT *** NEW FRACTURE RISK GUIDELINES CAROC 2013 REVISED ***:
10 year fracture risk (CAROC 2010): In 2010/2013, the Canadian Association of Radiologists and the Osteoporosis Society of Canada (CAROC) updated guidelines including a “Ten Year Fracture Risk” determination. This applies only to those =>50y (both male and female).
Categories are: LOW (<10%), MODERATE (10% to 20%), or HIGH (>20%). This predicts fracture risk of the hip, spine, forearm or proximal humerus, based ONLY upon the T-score of the FEMURNECK, taking AGE and SEX into account derived from a white female reference database. PREVIOUS guidelines required the determination of 10 year fracture risk based upon the lowest T-score found in all of the femur and spine areas, and therefore a change in risk category when comparing to past examination may not indicate a significant change in density. Instead refer to specific density change comments. No risk assessment available for individuals 85yo.
Individuals with fragility fracture after age 40 or systemic glucocorticoid therapy >7.5 mg/day > 90 days total in past year have at least moderate fracture risk. If both of these factors occur together, the risk is high.
Individuals with fragility hip or vertebral fracture after age 40 or 2 or more fragility fractures after age 40 have high fracture risk regardless of BMD result.
Individuals with lumbar spine T-score lower than -2.5 significantly worse than femur neck T-score have moderate fracture risk.
Fracture risk may be lower than calculated if osteoporosis drug therapy is effective.
Osteoporosis Canada - Tools and Resources
2010 Clinical Practice Guidelines for Diagnosis and Management of Osteoporosis in Canada:Summary
2013 CAR Practice Guidelines Technical Standard BMD Reporting Mayfair Mar 2014