3 ways to diagnose Osteoporosis
1. Based on Bone density scan (DEXA)
2. History of Fragility Fracture
3. High calculated risk of fracture
Bone density scan is not the only way to be diagnosed with osteoporosis. People often think of osteoporosis is a disease of decreased bone density. However, just as discussed in the previous section, osteoporosis is changes involving bone density and bone quality. A bone density scan does not tell us anything about your bone's micro-architecture or bone quality. It does tell us an overall measurement of the amount of mineralization you have. This measurement of bone is important, but does not tell us the whole picture. The goal of addressing osteoporosis is to reduce the risk of breaking bones. Each of the ways that we diagnose osteoporosis, the goal is to help identify who has a high risk of breaking bones. Let's go deeper into each of the diagnostic criteria.
Bone Density Scan
Bone density scan is assessed by a study called dual energy x-ray absorptiometry scan, or DEXA scan. This is a measurement of bone mineral density based on x-rays. The spine and one or more hips are usually assessed, and if those sites are not able to be assessed (due to hardware or arthritis) then the forearm can be assessed. The criteria for diagnosing osteoporosis based on DEXA scan was created by the world health organization in 1994. People with low bone density that meets criteria for osteoporosis have a high risk of fracture.
Bone mineral density with a DEXA results are reported as a “T-score” or “Z-score.”
The T-scores should be used in postmenopausal women and men over 50. T-scores compare your bone density to that of a healthy 30-year old. Z-scores compare your bone density to other people of your age, sex, and race and are used in males younger than 50 and premenopausal women.
A T-score greater than –1 is normal bone density
T-score between -1 and -2.4 indicates low bone mass (osteopenia)
A T-score equal or less than -2.5 indicates osteoporosis
Fragility fractures are broken bones that should not happen based on the mechanism of energy. They occur from low velocity trauma, such as a fall from standing height. Osteoporosis can be diagnosed in anyone who has a history of a fragility fracture, regardless of DEXA scan. Again, the DEXA scan does not look at bone quality. If someone breaks a hip from a fall, but their DEXA scan shows "osteopenia", it does not mean that person does not have osteoporosis. That person has osteoporosis, as the fragility fracture "trumps" the bone density scan. If you have broken one of what's supposed to be one of the strongest bones in your body, you have proven your bones are weak, and it is a strong indicator that you are at risk for more fractures. If you have broken a bone from a fall, all it takes is another fall to break another bone. People who have had fragility fractures have a high risk of future fractures. As an example, body sites that people break from a fall are associated with at least double the risk of another fracture in the future. If someone has a spine compression fracture, the risk of another spine fracture within the next year is 12 fold higher, and 5.7 fold higher in their lifetime.
This image shows spinal compression fractures on an MRI scan. Spinal compression fractures often go undiagnosed, but these types of fractures are strong predictors of future fracture risk. They can happen from falls as well as daily activities such as lifting a gallon of milk or bending over to tie your shoes.
Screening for these fractures is important. We can assess for these types of fractures on a DEXA scan if you are at high risk, with an x-ray of your thoracic and lumbar spine as part of your DEXA scan (the addition of this x-ray is called vertebral fracture assessment, or VFA).
Screening is also done in clinic if you have lost a significant amount of height. The average person loses 1.5 inches in their lifetime, largely due to arthritis and disc degeneration. We measure height very accurately at your appointment, and if anyone loses more than 1.5 inches from their tallest reported height, then we often times obtain an x-ray of the spine to assess for these types of broken bones.
High Calculated Risk of Fracture
This is not technically used to diagnose osteoporosis, however if your calculated risk of a fracture is high, guidelines recommend that you should be treated the same as osteoporosis. Think of this more as an equivalent to osteoporosis.
The risk of fractures is not just about your bone density. Factors that can affect your risk of future fractures include your age, sex, race, height, weight, family history of fractures, alcohol and tobacco use, medical history, and your bone density. Your information is entered into a computerized calculator that appropriately weighs all of these factors and calculates an accurate probability of you having a fracture in the next 10 years.
This calculation is included in your DEXA scan, if your are within the low bone mass or "osteopenia" range. The calculation that is used is called a FRAX score. FRAX stands for fracture risk assessment tool.
We calculate two different scores: 10 year probability of major osteoporotic fracture and 10 year risk of hip fracture.
A probability of a major osteoporotic fracture in the next 10 years of 20% or greater is considered high risk.
A probability of a hip fracture in the next 10 years of 3% or greater is considered high risk
Workup for osteoporosis
Workup for osteoporosis usually includes the following:
Comprehensive history (including past medical history (including fracture history), surgical history, social history, family history, assessment of dietary intake and exercise
Labs (to rule out other causes of bone loss/fractures)
X-rays to assess for spinal fractures