Bone Density T Score
Bone Density T-score measures your fracture risk compared to that of healthy young women and is considered by many experts to be best indicator of bone health. The World Health Organization (WHO) has defined the following T-score categories for white women:
• Normal bone Density: T-score better than -1
• Osteopenia: T-score between -1 and -2.5
• Osteoporosis: T-score less than -2.5
• Established (severe) osteoporosis
includes the presence of a non-traumatic fracture.
Comparing Bone Density Test Results
According to WHO, when the responsible committee developed these categories, it lacked sufficient data to create bone density T-scores for men or certain ethnic groups. It is important to realize that a bone density T-score is a measure of risk only. It does not predict a fracture.
There are different types of bone mineral density (BMD) testing equipment. Bone density test results can not be readily compared from one manufacturer’s scanner to another. Many health professionals recommend a central dual energy x-ray absorptiometry (DXA) machine to diagnose hip and spine bone loss, especially in patients susceptible to having osteoporosis.
Other BMD scanners provide bone density T-scores that may lack the reliability of DXA machines. These include QUS, (using ultrasound waves) and other radiation emitting equipment such as pQCT, pDXA and QCT. Finally, there is BMD equipment suited for initial screening of bone loss. The GE® Lunar densitometer is an ultrasound scanner that calculates heel bone density as a surrogate for the hip bone. This type of scan is not reliable enough for monitoring the bone benefit of a medication, exercise program or effective calcium supplement such as AdvaCAL over time.
In the 1970’s – 80s, bone density machines used different kinds of measurement units, so bone density T-scores were not applicable. Rather Z-scores were calculated to allow comparisons to normal people subgroups. Eventually, enough data was collected so bone density Z-scores could be measured against large sub-populations.
Your Z score, while not as critical as the bone density T-score, is also a statistical measure. It calculates the number of standard deviations above or below what's normally expected for someone of your age, sex, weight, and ethnic or racial origin. This is helpful because it may show – with a score below 1.5 – that you have a form of osteoporosis due to factors not related to aging. Your doctor would then try to determine an underlying cause for your low bone mass. If your doctor can identify a cause, that condition can often be treated and the bone loss slowed or stopped.
According to other leading health organizations, doctors typically measure BMD in the hip and spine. There are three reasons. First, these bones are likely to fracture. Second, fractures of these bones may cause an extended recovery time, pain and disability. Finally, BMD test results in the hip and spine may also be a precursor of future fractures elsewhere.
Don’t try to interpret your BMD results alone. Your doctor and you together can judge your progress over time following a given bone-building regime. He or she can also suggest adjustments to that regime, based on various bone related measures such as your bone density T-score.