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Controversial aspects of NORIP

Controversial aspects of NORIP. Peter Felding Copenhagen General Practitioners’ Laboratory. Common Nordic Reference Values, Session 15, NFKK 24 – 27 April 2004. Controversial aspects of NORIP. Selection of reference individuals The sample material

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Controversial aspects of NORIP

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  1. NORIP, Malmø 27/4-2004 Controversial aspects of NORIP Peter Felding Copenhagen General Practitioners’ Laboratory Common Nordic Reference Values, Session 15, NFKK 24 – 27 April 2004

  2. NORIP, Malmø 27/4-2004 Controversial aspects of NORIP • Selection of reference individuals • The sample material • The analytical measurements and the correction with CAL Target /Cal measured • Deviating new reference intervals • Haematology -use of EDTA in different forms • Reference intervals- not decision limits

  3. NORIP, Malmø 27/4-2004 The concept of reference values* • Reference individuals constitutes a • Reference population from which is selected** a • Reference sample group on which are determined ** • Reference values on which is observed a • Reference distribution on which are calculated • Reference limits that may define • Reference intervals (with which the patient result can be compared) *From J Clin Chem Clin Biochem. 1987 May;25(5):337-42. ** These are the controversial parts in NORIP

  4. NORIP, Malmø 27/4-2004 How to select the reference sample groups? General aspects* General population Reference population (unknown) A B A posteriori selection: Ideally random recruitment from the general population to form an initial sample group followed by exclusions A priori selection: Ideally random selection from the reference population or defined subgroups in the reference population Reference sample group/subgroups *Inspired by Clinica Chemica Acta,170 (1987) s3-s12 The final reference sample subgroups (after exclusions and partitioning) should represent the corresponding subgroups in the reference population. The first selection of individuals from the general population (A) or from the reference population (B) therefore ideally should be random and all selected individuals used as reference sample group or for further random or total selection to subgroups according to criteria for exclusions or partitioning. NORIP deviated from both these procedures.

  5. NORIP, Malmø 27/4-2004 Selection of the reference individuals in NORIP: All healthy Nordic adults (reference population) Representative? Random? 102 healthy adult subpopulations (around local labs) Representative? Random? 3000 healthy Nordic adults (reference sample group)

  6. NORIP, Malmø 27/4-2004 The reference sample groups in NORIP is characterised by: • Recruitment (more or less random) from 102 assumed healthy sub-populations somehow connected to participating laboratories in 5 countries.(Questions: Does the sum of these sub-populations fairly represent all healthy adults in Norden? And how random is the selection from each sub-population?) • Apriori fixed even relative distribution of individuals in 8 predetermined groups defined by age and gender. (Raise the problem: the selected individuals in the predetermined age-subgroups could theoretically for all relevant properties be composed as the corresponding age groups in the reference population, but the sum of the reference sample subgroups (all selected individuals) or later determined reference sample subgroups other than the predetermined could not because the age distribution in these later created reference sample groups does not reflect the age distribution in the corresponding reference populations.)

  7. NORIP, Malmø 27/4-2004 Controversial aspects of NORIP • Selection of reference individuals • The sample material • The analytical measurements and the correction with CAL Target /Cal measured • Deviating new reference intervals • Haematology -use of EDTA in different forms • Reference intervals- not decision limits

  8. NORIP, Malmø 27/4-2004 The sample material in NORIP(The preparation of the individuals and the sampling procedure are not considered controversial) • Frozen serum (all laboratories) • Fresh serum (optional) • Frozen Li-Hep plasma (10% of samples at all laboratories) • Fresh Li-Hep plasma (optional) • EDTA blood/buffy coat • (No gel) The control materials were fresh liquid frozen pooled unmodified or modified normal serum Question: Can reference intervals based on frozen material be used for fresh routine samples? What about plasma contra serum?

  9. NORIP, Malmø 27/4-2004 The sample material in NORIP continued The raised questions were apriori considered controversial but the use of fresh frozen serum was considered necessary in the chosen design. As it turned out there seemed to be no major problems connected to the use of fresh frozen serum samples including use of results from this material as reference values for patient results from fresh serum or plasma.

  10. NORIP, Malmø 27/4-2004 Controversial aspects of NORIP • Selection of reference individuals • The sample material • The analytical measurements and the correction with CAL Target /Cal measured • Deviating new reference intervals • Haematology -use of EDTA in different forms • Reference intervals- not decision limits

  11. NORIP, Malmø 27/4-2004 Determination of reference values Every initial measured result was produced by routine methods and for non enzymes then corrected with CAL Target/mean of CAL measured in the same series. This gives the corrected values high trueness at the mid reference interval level, but: • Eliminates the normally included between series analytical variation (this variation can be added locally to the recommended reference interval) and • May be a problem for the used routine methods, for which the initial measured value does not vary proportional with the true value (e.g. some or all Jaffé methods for Creatinine). The use of high and low controls (modified serum) could not totally eliminate or detect this problem, because only the unmodified controls can be considered fully commutable with patient samples.

  12. NORIP, Malmø 27/4-2004

  13. NORIP, Malmø 27/4-2004

  14. NORIP, Malmø 27/4-2004 Controversial aspects of NORIP • Selection of reference individuals • The sample material • The analytical measurements and the correction with CAL Target /Cal measured • Deviating new reference intervals • Haematology -use of EDTA in different forms • Reference intervals- not decision limits

  15. NORIP, Malmø 27/4-2004 Deviating new reference intervals Change of upper limit Enzymes Bilirubin Calcium Creatinine Potassium

  16. NORIP, Malmø 27/4-2004 New Nordic reference intervals for enzymes KPLL introduced the below changes 11 03 2004

  17. NORIP, Malmø 27/4-2004 The changes: Fewer pathological results for ALAT, CK ,GGT and Amylase More pathological results for Alkaline phosphatase and LDH

  18. NORIP, Malmø 27/4-2004 Reference intervalsnon-enzymes

  19. NORIP, Malmø 27/4-2004

  20. NORIP, Malmø 27/4-2004 Controversial aspects of NORIP • Selection of reference individuals • The sample material • The analytical measurements and the correction with CAL Target /Cal measured • Deviating new reference intervals • Haematology -use of EDTA in different forms • Reference intervals- not decision limits

  21. NORIP, Malmø 27/4-2004 Haematology • Not all laboratories participated (most of the reference individuals were from Sweden and Finland) • No common control/calibrator • Correction for dilutions due to EDTA in different forms. Dry form recommended. • Influence of tobacco (Lkc and other), age (Hb?), gender (Trc?) • Number of decimals (EVF) However, the final values seem uncontroversial (Upper limit 8,8 10E9/l for Leukocytes may be an exception. 10 or 11 10E9/l are presently more used)

  22. NORIP, Malmø 27/4-2004 Reference intervalsHaematology1800 ref. individuals from mainly Finland and Sweden

  23. NORIP, Malmø 27/4-2004 Controversial aspects of NORIP • Selection of reference individuals • The sample material • The analytical measurements and the correction with CAL Target /Cal measured • Deviating new reference intervals • Haematology -use of EDTA in different forms • Reference intervals- not decision limits

  24. NORIP, Malmø 27/4-2004 Health related reference intervals • Reference intervals describe the distribution of results from healthy individuals. They usually include 95% of these results. • They are created within the profession of clinical chemistry.(The traditional “owner” and decider has been the local laboratory because the intervals to some degree has been considered method specific) • They are still the most frequently used reference for patient results. In particular for properties requested with more than one indication (or with more than one decision limit)

  25. NORIP, Malmø 27/4-2004 Medical decision limits • Are created using patients and often? common for all analytical methods. • Are used to allocate patients to diagnosis, other investigations, treatments, change of treatment, public support, groups of prognosis etc. • Can be inside or outside the corresponding health related reference interval. • The same property can have several decision limits (because of use in different clinical situations or because of different recommendations). • They typically change with more knowledge without change in measured properties or patients (cholesterol!) • To use them the clinical situation must often be know • The medical societies and the clinicians are the “owners” or deciders.

  26. NORIP, Malmø 27/4-2004 Reference intervals as decision limits • Any “test” using a reference interval limit as diagnostic decision limit has a specificity of 95% (or 97,5%) for any disease i.e. the proportion of healthy persons with a ”healthy” test result is 95% (or 97,5%). • The corresponding sensitivities of the test for a variety of diseases are in many cases known but might not be relevant because the relevant diagnostic decision limit probably is not a reference interval limit.

  27. NORIP, Malmø 27/4-2004 Therapeutic intervals • Are subgroups of decision limits • Can relate to drug concentration or • Other properties influenced by drugs or other treatment (INR, HbA1c, Glucose?)

  28. NORIP, Malmø 27/4-2004 End of show Thank you for your attention Any questions?

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