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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