About two weeks, after I fractured my shoulder, I got a phone call from Kaiser Permanente, the health system where I get my care. The woman on the line identified herself as being part of my medical center’s Bone Health team. She said they were calling me because I had sustained a fracture that is suggestive of low bone density. She called it a fragility fracture. Other fragility fractures include vertebral fractures, fractures of the neck of the femur (a.k.a. hip fractures), and Colles fractures of the wrist. She said Kaiser scans its records for patients with these types of fractures so they can bring them in to evaluate their bone health.
My first reaction was “I am not fragile, I just tripped and fell.” But the Bone Health lady pointed out that people with normal bone health don’t usually fracture their big bones (humerus or femur) when they fall from a standing height. She said I needed to come in for a bone density test and blood tests to measure my vitamin D level (amongst other tests) to determine my risk of fragility fractures.
I was impressed. I am a long time fan of population health and have seen health plans and provider groups use it to proactively reach out to people with diabetes, heart failure, and asthma. But, I have never come across a population health program that targets osteoporosis even though, according to the National Osteoporosis Foundation, 54 million Americans have the disorder. Not only that, but 1 in 2 women and 1 in 4 men over the age of 50 will break a bone due to osteoporosis. Think about that for a minute! That’s an awful lot of people who will experience the pain, suffering, and cost of a big bone fracture that perhaps could have been prevented if their low bone density had been detected earlier.
Bone mineral density
Until recently, bone density tests—also called Bone Mineral Density (BMD), DXA, or DEXA (for dual-energy X-ray absorptiometry) test—were considered the gold standard to make the diagnosis of osteoporosis. The results of the BMD are still very important in making the diagnosis of low bone density (osteopenia or osteoporosis) and predicting the risk of fractures, particularly when used in conjunction with a bone fracture risk prediction tool, such as the World Health Organization’s FRAX tool. BMD tests are also used to assess changes in bone density over time and to monitor the effects of treatment.
The BMD machine works by firing X-rays from two different sources through the bones that are being tested towards a detector. The use of two different X-ray sources rather than one allows a more accurate reading of bone density. Mineralized bone blocks a certain amount of the X-rays. The denser the bone is, the fewer X-rays get through to the detector.
It is important to note that a BMD test is not the same thing as a bone scan that may be used to look for other types of abnormalities in your bones, such as metastases from cancer, infection, or inflammation.
There is no special preparation required for the test, although you should let your physician know ahead of time if there is a possibility you are pregnant or if you recently had a barium exam or received an injection of contrast material for a CT or radioisotope scan.
When you arrive for testing, you will be given a form to fill out that looks something like this. Information from this form will be used to calculate your overall fracture risk as will be explained below.
You will be asked to remove any jewelry and change into a hospital gown. Then, you will be positioned on your back on a special examination table. For part of my exam, I had a rectangular-shaped foam pillow placed under my knees and I was asked to remain very still while the machine was actively scanning the bones of my back (the vertebrae) and hip. Some people will also have scans of their wrist as well. The total time for the test—scan time plus repositioning time—is about 10 to 20 minutes, depending on which parts of your body are being examined. I was walking back to my car 20 minutes after I checked in for the test—and that included stopping at the lab for some blood tests.
Understanding the results
The data from the detector is sent to a computer which calculates a score of the average density of the bone in grams/cm². The computer program compares your score to groups of people of the same ethnicity and gender to calculate two different scores, a T-score and a Z score. When you get the results (and you should ask for a copy of the full report) it will look something like this:
“A bone mineral density (BMD) measurement was performed of the L1-L4 vertebrae and the proximal femur (total femur, neck, trochanteric, and intertrochanteric region) using a Hologic Dual Energy X-ray Absorptiometry Model Discovery C machine.”
You will want to know the name and model of the machine as it is important in determining your fracture risk. It is also important for your clinician to know this information because the results may vary by type of machine used. Comparing the results to a prior test done on a different make and model of machine can be problematic. The test result will also describe the measurement values and the comparison group:
The test result describes the measurement values and the comparison group:
“BMD values were determined in gms/cm² and compared to a young normal
reference population (T-score = standard deviations (SDs) below or above the young normal mean), and to an age-matched normal reference population
(Z-score = SDs below or above the age-matched normal mean).”
The T and Z scores are both important when interpreting the results and deciding if you need treatment. The T-score compares your bone density to that of young normal individuals. Bone density peaks somewhere between 18-35 years old. After that, there is a steady loss of bone that accelerates after menopause and doesn’t slow down again until the age of 70 or so. The T-score tells you how much bone you have lost compared to an average peak value of young healthy individuals of the same sex and ethnicity. The Z-score compares your bone density to that of people of the same gender and ethnicity and approximately your same age. If this score is lower than the reference population, it suggests you are losing bone faster than the average for your peers. This alerts you and your doctor that something other than “normal” bone loss due to aging may be going on. For example, that bone loss related taking certain kinds of drugs, such as glucocorticoids, aromatase inhibitors, or certain types of anti-epilepsy drugs. This type of osteoporosis is referred to as secondary osteoporosis (secondary to a factor other than aging).
“Reference BMD values for the hip were derived from the NHANES data and for the spine from the Hologic reference data. According to the WHO, criteria osteoporosis is defined by T-scores but you should note that these are only defined for a Caucasian female 65 years or older.”
According to an excellent review of best practices for Bone Mineral Density testing published in Volume 19 of the 2016 Journal of Clinical Densitometry (yes, there is such a journal),
“Manufacturers are advised to use National Health and Nutritional Examination Survey III young adult Caucasian female BM data as the reference standard for femoral neck and total proximal femur T-score calculation.”
They can use their own reference data for lumbar spine T-score calculation. This review makes it clear that, as is true of most things in medicine, the devil is in the details. BMD tests need to be performed properly with well-trained technicians and properly calibrated and maintained machines. The interpretations must be done by people who know what they are doing and understand the critical importance of applying the correct comparisons. Embarking on treatment for osteoporosis requires that best practices be followed.
“A normal T-score is between 0 and -1.0. Osteopenia is defined as a T-score of -1.1 to -2.4. Osteoporosis is defined as a T-score of less than -2.5.”
Assessment of risk of fragility fractures
The T-score is only one piece of information that is used to estimate the risk of having an osteoporotic fracture over the next 10 years. Although there are several fracture risk predictors available, the one most commonly used is the World Health Organization’s FRAX tool. You can find an online version of the tool here: www.shef.ac.uk/FRAX
The tool calculates risk based on age, gender, BMI, and the clinical risk factors reported obtained from a questionnaire filled out at the time of the bone density test (see above). You can get an estimate of your risk even if you have not yet had your BMD test. But it is more accurate if you are able to include the measured density of your femoral neck—note that you will be asked to include the make of the machine used for your test.
The clinical risk factors considered by FRAX are:
- a previous fracture
- a parent who fractured a hip
- current smoking
- use of glucocorticoids
- rheumatoid arthritis
- a diagnosis of secondary osteoporosis
- alcohol intake greater than 3 units per day
This is how this information appeared in my report:
“10-year fracture risks were calculated using the World Health Organization FRAX tool based on the age, gender, BMI, clinical risk factors reported by the patient, and the BMD of the femoral neck measured. Clinical risk factors considered by FRAX are: previous fracture, parent fractured hip, current smoking, glucocorticoids, RA, 2nd osteoporosis, and 3 or more alcohol units per day.”
The FRAX score (estimated risk of having an osteoporotic fracture over the next 10 years) is reported as two different risks: The percent risk for any major osteoporotic fracture and the percent risk for a hip fracture.
Who should be considered for treatment?
My report also contained the following language about treatment:
“National Osteoporosis Foundation recommends to consider initiating therapy:
1) postmenopausal women and men age 50 and older with hip or
vertebral fractures, or fragility fractures
2) DEXA BMD T-scores ? -2.5 (after excluding secondary reasons for
3) For osteopenic patients: 10-year hip fracture probability ? 3% or a 10-year major osteoporosis-related fracture probability ? 20% based on the US-adapted WHO absolute fracture risk model FRAX…
…all treatment decisions require clinical judgments and consideration of clinical risk factors that may or may not have been captured in the FRAX model and possible under-or-over estimation of fracture risk by FRAX.”
Missing from the report, but very important is the patient’s preference. Failure to take this into account may be one reason why so many people refuse to initiate treatment, fail to take medications as prescribed or discontinue treatment that could be beneficial. We will, of course, dive into all of the issues related to the treatment of osteoporosis in a future post.
Here are some articles that you may find helpful:
- Evaluation and Treatment of Osteoporosis. Medical Clinic of North America, 2016; Vol 100 (2016) 807-826. It can be purchased here: http://linkinghub.elsevier.com/retrieve/pii/S0025712516000468
- Bone mineral density: testing for osteoporosis. Australian Prescriber April 2016; 39 (2) 35-39
- Best Practices for Dual-Energy X-ray Absorptiometry Measurement and Reporting: International Society for Clinical Densitometry Guidance. Journal of Clinical Densitometry: Assessment and Management of Musculoskeletal Health, 2016; 19 (2):127-140
Please leave a comment or contact me at firstname.lastname@example.org if you would like to share your personal journey with osteoporosis. Please do not leave comments asking for medical advice as that is best discussed with your doctor.