PEPFAR Quality Control and Method Validation Activity 8 Job Aid 1: Using TEA

Job Aid 1: Using TEA 813 Using Total Allowable Error (TEA ) in your Laboratory Total Error: TE is the total variation of your laboratory’s value from the Step-wise Approach from a Leading Expert i true value 1. Gather mean & SD data from all instruments in your Total Allowable Error: TEA specifies the maximum acceptable variation laboratory or integrated group HOOD05162002658134 Effective Date: 09/05/2017 from the true value; the amount of error that can be tolerated 2. Estimate true value (as average of in-lab instruments, if without invalidating the clinical usefulness of the result peer data not available) 3. Calculate Total Error in units and in percent of the True TEA is the 4th key number for SQC. Value for each QC sample for each analyte on each • It is test-specific instrument • Defines the acceptable performance limits for the test 4. Research potential sources of TEa based on the Stockholm hierarchy You may need to look at several sources to determine your TEA for a 5. Select best "attainable and defensible" TEa limit specific assay. • Select Professional Expert Publications, if available • Select Biological variation - if easily attainable AND Sources in descending order of priority (hierarchy of desirability): less than PT limits 1. Medical Decision Levels • Select PT limits - if available and BV is unattainable published, peer-reviewed information is available for glucose and cholesterol • Select Proficiency Testing (PT) Survey CV% x 3 only if limitation: often this information is not available the above sources are unavailable 2. Biological Variation • Use Tonk's rule only if the above sources are based on the expected percentages of variation within and between individuals unavailable limitation: because error is expressed as a percentage, these goals may be • Select 3x your median historical internal SD if other unrealistic at lower concentrations sources are unavailable 6. Choose a defensible TEa that allows a comfortable margin of error 3. Proficiency Testing Guidelines Criteria used by the organizers of PT schemes to determine acceptable Once the target value and TEA limits for each test and control performance concentration are established, comparing TE to TEA (TE < TEA ) allows you to: 1. 4. Proficiency Test Results Assess method performance 2. Check calibrations Using peer group’s median %CV x 3 limitation: peer groups do not cover the full reportable range; can vary 3. Evaluate the acceptability of new reagent lot numbers substantially between instruments and peer groups 4. Evaluate changes to the analytical system 5. Tonk’s Rule 5. Determine the size of change which must be detected [(Reference range span)/ 4 /mean of range]* 100% 6. Select appropriate QC rules 6. Current SD x 3 For some esoteric testing, no other source may be available i From Brooks, Zoe at Awesome Numbers