![]() In 1994 the World Health Organization defined the following categories based on bone density in white women: Furthermore, a person can have one T-score and Z-score at the femoral neck, another at the total hip, and another at the spine.Ĭlick to read more details about the relationships between T-score, Z-score and g/cm 2, including conversion formulas, data tables and some of the misconceptions about the interpretation of the scores. There are also different Z-scores depending on the group used as a reference (for example, the group could include everybody of the same age, or it could be limited to people with the same age, race, gender and weight). The Z-score is the number of standard deviations below an average person of the same age. There are different T-scores depending on which group of young adults were used as the reference (for example, Caucasian women, Hispanic men). The T-score is the number of standard deviations below the average for a young adult at peak bone density. Shown here is the classical bell-shaped curve with the percent of a population lower than that value. T and Z scores are based on the statistical unit of the standard deviation. The next sections will attempt to clarify these issues, such as T-score, Z-score and the redefinition of "normal". Here is a REFERENCE RANGE for CHILDREN by Kalkwarf.īone density results have been reported in a variety of ways that have been confusing to physicians and patients. The fracture risk calculator can be used to predict fracture risk from the DEXA results.īone density results in teenagers was published by an international collaboration. The bone density is important because it can help to predict the risk of getting a fracture. The lines show the average values, and for each age, race and gender a range of values occurs in the ordinary population ( Looker) The units are standardized bone density in (mg/cm 2). This graph shows how the bone density of the total hip decreases with age. High-resolution magnetic resonance imaging of the tibia or radius shows promise for allowing a "virtual biopsy" of the bone and can non-invasively follow bone structural changes, but this is also currently a research tool. Other Older methods that can measure bone density at the hand, radius or ankle include single energy absorptiometry, metacarpal width or density from hand xrays. Currently these are only available in research centers. High-resolution peripheral QCT (HR-pQCT) can be used on the radius or tibia to study in detail the changes in the cortical vs. In May 2013 QCT measurements were added to the FRAX website and they can be used to estimate fracture risk.Ĭlick to see table of T scores using the traditional QCT measurements compared to those using DEXA. This technique still does not have the large database that is available with DEXA. There are some newer machines which may have better precision. The QCT measurements decrease more rapidly with aging, so in older individuals the "T scores" can be more than 2 units lower than DEXA measurements. Radiation exposure is greater than with the other techniques. QCT Quantitative computed tomography of the spine must be done following strict protocols in laboratories that do these tests frequently in community settings the reproducibility is poor. Recently ultrasound measurements have been included in the FRAX fracture prediction tool, and they can be used to predict risk of osteoporotic fractures. ![]() This technique has not been used as often because there is not as much data about effects of medications. Although some have said that ultrasound measures the "quality" of bone, more careful studies suggest that it mainly measures the bone mass. Adding an ultrasound measurement to a DEXA does not improve the prediction of fractures. Ultrasound at the heel can predict hip fractures nearly as well as DEXA. Ultrasound Ultrasound measurements are usually performed at the calcaneous and it is not possible to measure sites of osteoporotic fracture such as the hip or spine. Here are more details about reading bone density printouts. Three companies manufacture these densitometers: Hologic, Norland, and Lunar. Older methods such as single photon absorptiometry do not predict hip fractures as well as DEXA. This is the method used to determine efficacy in the recent large clinical trials, and to characterize fracture risk in large epidemiological studies. Techniques DEXA Several methods are available to measure bone density, but currently the most widely used technique is DEXA (Dual Energy Xray Absorptiometry). How to read a DEXA printout, step-by-step.
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