Josiane Arnaud1, Jean-Philippe Weber2, Are desirable quality specifications for evaluating laboratory performances in external quality assessment schemes for copper, zinc and selenium in human serum or plasma attainable? Josiane Arnaud1, Jean-Philippe Weber2, Cas W Weykamp3, Patrick J Parsons4, Olav Mazarrasa5, Antonio Menditto6, Marina Patriarca6, Andrew Taylor7 1 – CHU de Grenoble, France; 2 – Institut National de Santé Publique, Québec, Canada; 3 – Queen Beatrix Hospital, Winterswijk, The Netherlands; 4 – New York State Department of Health, Albany, USA; 5 – Centro de Seguridad y Salud en el Trabajo, Santander, Spain; 6 – Istituto Superiore di Sanità, Rome, Italy; 7 – University of Surrey, Guildford, UK

Thematic Network Organizers of external quality assessment / proficiency testing schemes related to occupational and environmental laboratory medicine Conflicting conclusions at the participant level Different possibilities for organisation, statistical analyses, participant monitoring ISO 13528, EURACHEM, EQALM, ILAC, IUPAC, IFCC… TE EQAS consensus procedures Coordonnateur : Dr Andrew Taylor (University of Surrey)

Uncertainty evaluation Calculated (sample dependent)  Consensus participants’ standard deviation (after exclusion of outliers) Reference laboratory standard deviation Metrological laboratory standard deviation Defined (analyte and medium)  Defined by the law  Quality specification = QS

Quality specification criteria Must take into account:  Analytical possibilities (concentration range)  Expertise of laboratory  Biological individual variability  Overlaps between « normal » and pathological states Law recommendations (if any) EQAS role: laboratory licensing or education

Quality specification calculation Horwitz Equation : 0.02C0.8495 Fraser’s equation: 0.25(CV2intra+CV2inter)1/2 + z(0.5xCVintra) (100/4)* ref. range/mean ref range Tonk equation: Quality specification calculation

Quality specification calculation Fraser’s equation, 1999 Desirable total error % = 0.25 (CV2intra + CV2 inter)1/2 + z (0,5 CV intra) CV intra = intra-individual variability CV inter = inter individual variability z = 1.65 for a 95% probability level. Fraser CG. Scand J Clin Lab Invest 1999;59:487-90.

Individual Variability (published datas* on healthy populations) Copper Zinc Selenium intra 2.3 – 9.2 4.4 - 9.4 3.6 - 5.1 inter 12.2 - 16.9 4.1 - 10.7 13.0 - 13.9 *References Gallagher SK, et al. Clin Chem 1989;35:369-73 Gonzalez-Revalderia J, et al. Clin Chem 1990;36:2140-1. Sabban A. Thesis, University of Surrey, 2005. Lacher DA, et al. Clin Chem 2005;51:450-2.

Cu Zn Se quality specification Minimal QS*,% 12 15 Desirable QS*,% 8 10 Optimal QS*,% 4 5 *Desirable total error % = 0.25(CV2intra+CV2inter)1/2 + z(0.5xCVintra) Optimal = 0.5 Desirable. Minimal = 1.5 Desirable.

Uncertainty and concentration 0,00 10,00 20,00 30,00 40,00 50,00 60,00 70,00 Zn CV % (participants) Zn target concentration, µmol/l (consensus after exclusion of outliers) Minimal QS: 1.2 µmol/l  8 µmol/l Desirable QS: 0.8 µmol/l Optimal QS: 0.4 µmol/l Zinc

Cu Zn Se quality specification (low concentrations) Cutoff, µmol/l 7 8 0.6 Minimal QS, µmol/l 0.84 1.20 0.072 Desirable QS, µmol/l 0.56 0.80 0.048 Optimal QS, µmol/l 0.28 0.40 0.024

Quality specification evaluation

Method Sample concentration selection Cu, µmol/l 3.5 9 15 20 30 Nb participants 82 128 184 239 168 Se, µmol/l 0.25 0.5 1.0 1.5 3.0 69 101 95 143 97 Zn, µmol/l 8 144 156 228

Z-score = (xi-X)/(QS/2) Method Z-score Z-score = (xi-X)/(QS/2) where xi = participant’s result, X = target value QS = quality specification. QS is divided by two to be consistent with the ISO guide which states that performance is Satisfactory if Z-score 2 Unacceptable if Z-score > 2 Allows comparison of  samples

Cu, Zn and Se Z-score percentiles Results Cu, Zn and Se Z-score percentiles Minimal Cu Minimal Se Minimal Zn Desirable Cu Desirable Se Desirable Zn Optimal Cu Optimal Se Optimal Zn -8,00 -6,00 -4,00 -2,00 0,00 2,00 4,00 6,00 8,00 10,00 Z-score, percentiles

Unacceptable results, % Cu &Se 30 3 20 1.5 15 1.0 9 0.5 3.5 0.25 Concentrations, µmol/l Zn 20 15 8 % of Z-score>2

Discussion Participant value Target value TE EQAS Conclusion 22.0 20.0 NY Satisfactory BE Unacceptable Discussion

Discussion Fraser’s equation, 1999 Desirable total error % = 0.25 (CV2intra + CV2 inter)1/2 + z (0,5 CV intra) Limitations Literature agreement Pathological states Analytical possibilities Advantages Biological variability Sample and run independent

Discussion Imprecision, % Cu Se Zn Fraser’s QS, optimal (this work) 4 5 Fraser’s QS, desirable (this work) 8 10 Fraser’s QS, desirable (Ricos, plasma) 12 14.5 11 Fraser’s QS, desirable (Ricos, serum) 14 13.5 Analytical variability (ref. laboratories) 4.3 6.0 5.8 Analytical variability (participants) 10.1 17.4 14.7 Fraser’s QS, minimal (this work) 15 Ricos C et al. Scand J Clin Lab Invest 1999;59:491-500

Discussion : Comparison to current QS – Cu & Zn CA, FR : 0.08x + 0.4 BE, UK : 0.031x + 0.9 IT : 0.075x + 0.6 Cu NY : 0.1x Zn NY : 0.15x 0,00 1,00 2,00 3,00 4,00 5,00 6,00 7,00 8,00 10 20 30 40 50 60 Concentration, µmol/l QS, µmol/l Minimal Zn QS : 0.15x if >8 µmol/l Minimal Cu QS : 0.12x if >7 µmol/l

Discussion : Comparison to current QS - Se IT QS = 0.06x + 0.06 BE, CA, FR, UK QS = 0.06x + 0.07 NY QS = 0.2x 0,00 0,10 0,20 0,30 0,40 0,50 0,60 0,70 0,80 0,90 1,00 2,00 3,00 4,00 5,00 Se concentration, µmol/l Se QS, µmol/l Minimal QS = 0.12x if x> 0.6 µmol/l

Conclusion Patient’s diagnosis and follow-up Reliable determinations Participant laboratory TE EQAS objective quality specification Analytical performances Individual variabilty harmonisation

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