Levey-jennings Information and Courses from MediaLab, Inc.
These are the MediaLab courses that cover Levey-jennings and links to relevant pages within the course.
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|Levey-Jennings Quality Control Charts|
Quality control charts are used to record the results of measurements on control samples, to determine if there are systematic or random errors in the method being used. The most common type of chart is the Levey-Jennings chart.There should be a separate control chart for each method being monitored, and separate charts for normal and abnormal controls. The mean and standard deviation of the control being used should be noted on the chart. These should be determined based on at least 20 measurements over 20 days. Here is an example of a Levey-Jennings chart. Each time the control is tested, the result is marked on the chart at the appropriate standard deviation level. For instance, if the mean for a control is 15 and the standard deviation 5, if you test a control, and get a value of 22.5, the chart is marked at +1.5 SD for that day.
|Levey-Jennings Control Charts|
Daily documentation and evaluation of quality control is vital to detection of errors. One of the most commonly used methods for documentation is the Levey-Jennings control chart (L-J chart). In 1931, Dr. Walter Shewhart, a scientist at the Bell Telephone Laboratories, proposed the application of statistical-based control charts to monitor industrial manufacturing processes. In 1950, S. Levey and E.R. Jennings applied Dr. Shewhart's control charts to the clinical laboratory.
|What is a Levey-Jennings Chart?|
The Levey-Jennings chart usually has the days of the month plotted on the X-axis and the control observations plotted on the Y-axis. On the right is the Gaussian or "bell-shaped" curve turned on its side to show the correlation of the curve to the chart (ie, fewer data points should appear on the upper and lower extremities of the chart, since the "bell" is thinner farther from the mean). By observing the data plotted in the L-J chart, we can determine if test results are in control and accurate, or if test results are not in control and consequently unacceptable. Use of the Westgard, Cumulative Summation Rules, and the Youden plots will help establish an effective error-detecting scheme.
|CUSUM Example: Plotting Control Data|
To illustrate the use of CUSUM in the laboratory, we'll use daily control values for glucose testing. In the example laboratory, testing is not performed on weekends, explaining the lack of data on days 1, 7, and 8.First, we'll list daily control values under "daily results." Then, we'll calculate mean by using formula A. Next, we can find the difference from the mean for each result, and square that result for the two relevant columns. Using all of the squared differences from the mean, we can find the standard deviation using formula B. Using the mean from formula A and the standard deviation calculations from formulas B and C, we can plot our data points on the Levey-Jennings chart. Formula D helps us calculate the coefficient of variation (CV), which expresses SD as a percentage of mean value and is more reliable for comparing precision at different concentration levels. The lower the CV the greater the precision.
|CUSUM and Westgard Rules|
Looking at the Levey-Jennings chart you will notice that the plots correspond with the Westgard rule 41s. What type of movement and error do you think this reflects?
|Which Westgard rule violation is illustrated by these normal and abnormal control charts?||View Page|
|The Levey-Jennings charts on the right represent two levels of control for an analyte. Do they show acceptable quality control results?||View Page|
|Does the Levey-Jennings chart to the right show acceptable quality control results?||View Page|
|A Quality Control Exercise|
For this problem, you may need to work off-line. After you have evaluated the data on the following page, return to the course and answer the accompanying questions. Problem You are the only full-time employee at a small clinic's laboratory. You use an assayed control for your glucose determinations. The manufacturer's printed values for the present lot number are: Level 1 Control Mean: 72 mg/dL Standard deviation: +/- 2 mg/dL Level 2 Control Mean: 281 mg/dL Standard deviation: +/- 12 mg/dL The table on the next page shows the control results for the first twelve days of testing for the month. Plot your QC results on a Levey-Jennings chart and evaluate your data.