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Understanding Bone Density T-Score and Z-Score

Author Zizzur Staff. Published on October 17, 2011 - 1:08 am (686 views — 402 words)

If the possibility of future injuries and risks are palpable, it is imperative that the patient goes through the bone mineral density (BMD) test to determine the bone health at that particular instance. The findings from the test expressed as T-score and Z-score are significant because they work as the backbone of the treatment program to manage the medical case of the patient. The concern remains: how are these bone density T-score and Z-score analyzed?

In 1994,the public saw the appraisal of existing information pertaining to the testing of bone density from among the different nations by the World Health Organization (WHO). In order to have a common approach in the analysis and understanding of bone density findings, the T- and Z-scores were adopted basing on a comparison with a standard that has normal bone density. Negative values are indications of bone loss, osteopenia or osteoporosis.

In what context can the bone density T-score be taken? The T-score is actually a mathematical expression showing the standard deviation from the mean of the sample taken from a particular reference population. This is done by comparing the bone density of the subject to that of the standard which is another adult, usually a healthy 30 year-old, and of the same gender. The difference is used to signify the health condition of the bones. T-scores of +1.0 through +4.0 indicate very high bone biomass and -1.0 through +1.0 as normal. Low bone density is indicated by values below -1.0. Subjects with T-scores -1.0 through -2.5 usually have osteopenia while those with T-scores lower than 2.5 usually have osteoporosis.

What can the Z-score indicate? The Z-score is actually derived by comparing the bone density of the patient to another adult that has the same sex and age. The assumption is that the standard used manifest healthy bone mass. When findings are shown to be Z-score lower than -2.0, that is a sign about the possibilities of low bone densities and rapid bone loss. Z-scores are important because they can point to the existence of secondary osteoporosis caused by other diseases and treatments.

Using bone density T-score and Z-score provide useful basis in establishing the true state of bone health of a patient. Their examination is critical for all stakeholders. The understanding of which is as essential to the doctor as to the patient for successful treatment and management of osteoporosis and the prevention of future risks.