finals - chem

• Quality Control Chart


  Used to observe values of control materials over time to determine reliability of the analytical method
• Quality Control Chart


  • Utilized to observe and detect analytical errors such as inaccuracy and imprecision
• Gaussian Curve (Bell-Shaped Curve)


  Obtained by plotting the values from multiple analyses of a sample
• Gaussian Curve


  • When the data set can be accurately described by the Standard Deviation and Mean
  • A population probability distribution that is symmetric about the mean
  • Focuses on the distribution of errors from the analytical method rather than the values from a healthy or patient population
  • The total area under the curve is 95 or positive/negative 2 Standard Deviation
• Cumulative Sum Graph / Cusum


  Calculates the difference between QC results and the target means
• Cumulative Sum Graph / Cusum


  • Common method: v-mask
  • Gives the earliest indication of systematic errors (Trend), and can be used with the l3s rules
  • Very sensitive to small, persistent errors that commonly occur in the modern, low calibration-frequency analyzer
  • Results are out of control when the slope exceeds 45 degrees or a decision positive or negative 2.7 Standard Deviation is exceeded
• Youden or Twin Plot


  Used to compare results obtained on a high and flow control serum from different laboratories
• Youden or Twin Plot


  • Displays the results of the analyses by plotting the mean values for one specimen on the y-axis (ordinates) and the other specimen on the x-axis (abscissa)
  • The points falling from a center but on the 45 degree line suggest a proportional error, and points falling from the center but not on the 45 degrees line suggest a constant error
• Shewhart Levey - Jennings Chart


  Most widely used QC chart in the clinical laboratory
• Shewhart Levey - Jennings Chart


  • Allows the laboratories to apply multiple rules without the aid of a computer
  • A graphic representation of the acceptable of variation in the results of an analytical method
  • Easily identifies Random and Systematic errors
• Errors observed on LJ Chart


  • Trend - formed by control values that either increase or decrease for 6 consecutive days
  • Shift - formed by control values that distribute themselves on one side or either side of the mean for 6 consecutive days
  • Outliers - control values that are far from the main set of values
• Westgard Control Rules


  • 12s - used a rejection or warning rule when one control result exceeds the mean Plus or minus 2SD; for screening purposes
  • 13s - one control result exceeds the means Plus or minus 3S; it is effective in determining random errors
  • 22s - the last 2 control results exceed either the mean Plus or minus 2S; respond most often to systematic errors
  • 41s - the four consecutive control results exceed either mean Plus or minus 1s; respond to systematic errors
  • R4s - the range or difference between the highest and lowest control result within an analytical run exceeds Plus or minus of 4SD; responds to random error or increase imprecision
  • 10x - ten consecutive results are on the same side of the target mean; systematic errors