Abstract
Although much has been written about quality control procedures in densitometry, many of these articles have been concerned with data collection in clinical research rather than patient data collected as part of medical care. Quality control, while absolutely necessary in clinical research, is no less necessary in clinical practice. The original indications for bone mass measurements from the National Osteoporosis Foundation published in 1989 and the guidelines for the clinical applications of bone densitometry from the International Society for Clinical Densitometry published in 1996 called for strict quality control procedures at clinical sites performing densitometry (1,2). The Canadian Panel of the International Society for Clinical Densitometry published specific guidelines for quality control procedures in 2002 (3). Such procedures are crucial to the generation of accurate and precise bone density data. When quality control is poor or absent, the bone density data may be incorrect. The interpretation made by the physician based on that incorrect information would be in error. The medical management of the patient may be adversely affected. The patient will also have been exposed to a small amount of radiation inappropriately and wasted time and money. In clinical trials, the results from hundreds or thousands of individuals are usually averaged and conclusions based on the average values. Small errors in machine performance are made insignificant by the averaging of so many results. In clinical practice, this luxury does not exist. Decisions are made based on one measurement from one patient, which means that strict quality control in clinical practice is even more important than in clinical trials. In spite of inherently superb accuracy and precision in today’s densitometers, alterations in the functioning of the machines can and will occur. Quality control procedures to detect these alterations in machine function should be utilized by every clinical site performing densitometry regardless of the frequency with which measurements are performed.
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Notes
- 1.
The Canadian Panel of the International Society for Clinical Densitometry represents the International Society for Clinical Densitometry in Canada and oversees the society’s programs in Canada.
- 2.
Dr. William Andrew Shewhart (1891–1967) as a scientist with Western Electric; devised the basis for the application of statistical methods to quality control. In 1931, his book, Economic Control of Quality of Manufactured Product, was published in which he presented his methods for statistical sampling.
- 3.
In this context, z-score has nothing to do with reference population BMD data. It is simply the number of standard deviations above or below the average value.
- 4.
Linear regression involves the development of a mathematical model in order to predict one value from the measurement of another. Such models are useful but they are never perfect. Many statistical calculators or software programs can be used to calculate the regression equation.
- 5.
The standard error of the estimate (SEE) is also known as the standard deviation from the regression line. It is an estimate of the variability about the line of means predicted by the regression equation.
- 6.
The 95% confidence interval describes the range of values within which we can be 95% confident that the true value actually lies.
- 7.
The ISCD cross-calibration tool is available in the Members Only section of the web site at http://www.iscd.org. It can be downloaded and runs within Microsoft Excel.
- 8.
See Chapter 11 for a discussion of the LSC.
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Bonnick, S.L. (2010). Quality Control. In: Bone Densitometry in Clinical Practice. Current Clinical Practice. Humana Press, Totowa, NJ. https://doi.org/10.1007/978-1-60327-499-9_4
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