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LABQUALITY
Om Analytisk Imprecisionoch
Analysers Totalfel
Vårmöte Luleå 250505
Teddy Weber
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Do the current target limits of EQA schemes serve participants well enough?
interpretation of results
conclusions on analytical performance
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Target limits
= target value ± total error
imprecision biasmethod group mean
orreference method value
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- clinical needs- state of the art- statistical methods- within- and between-subject biological variation- suitable part of reference intervals
Different considerations can lead to different target limits. The priority may be maximal allowable error or educational quality goals.
Approaches for defining permissible total error
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• imprecisionless than a half of the within-subject biological variation
• biasless than ¼ of the biological variation (within + between-
subject variation)or
less than 1/16 of the reference interval
• Biological variation
• Common reference intervals
Components of total error are based on
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Target value ± (bias + 1.65 * imprecision)
Target value ± (¼ CVbt + 1.65 * ½ CVbw )
bt = total biological variationbw= within-subject biol.variation
The target limits are set so that when the methods are performing correctly, the result will be within the target limits with 95% probability
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sometimes
biological variation approach would lead to too demanding analytical goals (e.g. Na total error 0.9%)
total error 2%
CV%-target from the analytical performance
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sometimes
biological variation approach would lead to too wide analytical goals (enzymes e.g. CK 27%, ALT 36%)
CV%-target for enzymes from the analytical performance
total error 12%
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Examples of Quality specifications in Labquality clinical chemistry surveys
Albumin 5 % Ca-Ion 3 % CRP 15 %ALP 12 % Cholesterol 5 % Free T4 12 %ALT 12 % Chol-HDL 10 % Sodium 2 %Bilirubin 12 % CK 12 % Triglyserides 15 %Calcium 3 % Creatinine 8 % TSH 12 %
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Labquality´s target limits are educationaland not administrative.
Labquality´s target limits are quite tight.
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