The most common errors in the densitometric diagnosis of osteoporosis.

A review of world literature on the subject indicates that, given the present state of our knowledge, and the technological possibilities and availability of the apparatus, the most useful method for the evaluation of bone metabolism, especially the diagnosis of osteoporosis, is dual energy X-ray absorptiometry (DEXA). However, this method is not free of errors that can exert a negative impact on the final results of examination. On the basis of heir own experience, the authors have presented here the most common errors encountered in the densitometric technique. A DPV-L densitometric apparatus (Lunar Corporation) was used in this research. Errors in densitometric testing are divided into three groups: those dependent on the object investigated, those dependent on densitometric data analysis, and others. In the first group we took into account factors which can lead to either overestimating (+) or underestimating (-) the final test results: degenerative changes (+), scoliosis (+), the presence of foreign bodies, such as metal (-), status post fracture (+), the presence of pathological structures (+ or -), osteoporotic fractures (+), and incorrect arrangement of the investigated object (+ or -). Errors in data analysis included erroneous data entry regarding the patient's age, height, body mass (affecting the value of the Z-score), and sex (distorting the T-score and the Z-score), and incorrect settings regarding the measurement field. Other errors to densitometric technique included failure to calibrate or improper calibration of the measurement apparatus and errors in computer programming. Individual errors were responsible for falsifying results from 1 to 37%. If several of these errors are accumulated, the accuracy of examination may change more than 100%. Densitometric examinations of the lumbar spine are the most subject to error. The repeatability of the results generated by the DEXA apparatus (as stated in the equipment specifications) ranges for particular skeletal regions from 0,9% to 2,5% of the coefficient of variance, while the precision ranges from 3% to 5%. This means that even if we follow the strictest guidelines for test procedures, the margin of error is still several percent. We also cannot exclude the impact of errors of the three types listed above on the final results. We are convinced that the DEXA method is an excellent instrument for the diagnosis of osteoporosis (in static bone evaluation). However, its value diminishes in monitoring dynamic changes in bone tissue, even at 1-2 year intervals.