Quality Control

TERMS TO REMEMBER:

• Quality: a feature/characteristic of a product which meets the expected criteria of a consumer (customer).
• Control: a solution that resembles a human sample that is used for QC purposes only
• Standard: a colorless solution with known concentration of substances used for calibration
• Specificity: defined as the ability of a method to measure the analyte of interest ONLY.
• Sensitivity: defined as the ability of a method to measure analytes even at its lowest concentration
• Accuracy: nearness of measured value to that of the target value
• Precision: nearness of measured values to each other
• Diagnostic specificity: defined as the ability of a method to detect a population of individuals absent of a disease process
• Diagnostic sensitivity: defined as the ability of a method to detect a population of individuals having the presence of disease
• Intralab QC (internal QC): control samples are run simultaneously with a patient to ensure reliability of methods and result. Used for daily monitoring of accuracy and precision of method used. Detects random and systematic errors.
• Interlab QC (external QC): laboratories are given samples with unknown concentrations for them to test and results are compared with other laboratories thus maintaining “long-term accuracy” to methods utilized.
  • Results difference of greater than 2SD indicates disagreement with other lab included.
• Mean: average of a set of values (mean = Σx/n). Measures central tendency.
• Median: midpoint of a set of values
• Mode: the most frequent among all values/data
• Range: Simplest expression of spread or distribution
• Standard Deviation: it is defined as the measure of dispersion of values to that of the mean. Most frequent used measure of variation.
• Coefficient of variation: mean expression in percentile. Index of precision
• Variance: square of SD. V=SD²
• T-test: this is used to assess if there is a statistical difference between the means of 2 groups of data
• F-test: this is used to assess if there is a statistical difference between the SD of 2 groups of data
• Shewhart Levey-Jennings Chart: most widely used QC chart
• Trend: six or more consecutive values that either increase or decrease gradually (will cross the mean) – main cause: reagent deterioration
• Shift: six or more consecutive values that are distributed on one side or other side of the mean (does NOT cross the mean) – main cause: improper instrument calibration

• Delta check: used to check if there are significant differences between present set of values to that of past values on the sample of same individual.
• Six Sigma: a way of improving product processing to eliminate defects