Proceedings of 9ICP

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1 Proceedings of 9ICP - 7 Evaluation of serological diagnosis capacity for paratuberculosis using proficiency testing by interlaboratory comparison at the level of veterinary laboratories from Romania in 6 Petriceanu G, Radulescu RA, Ragalie A, Guţu E, Tănăsuică RN Institute for Diagnosis and Animal Health Romania Sanitary Veterinary and Food Safety Direction Bucharest, Romania INTRODUCTION Paratuberculosis (Johne's disease) is a disease of domestic and wild ruminants, caused by Mycobacterium avium subsp. paratuberculosis, culminating with chronic enteritis (Anon., b). In 6 year, Immunology Department from Institute for Diagnosis and Animal Health, organised a paratuberculosis serological diagnosis capacity testing through proficiency testing by inter-laboratory comparisons of veterinary laboratories in Romania. The aim of this testing was the improvement of quality system for testing and evaluation of laboratories by statistic analyses, studying new classification models of the veterinary laboratories depending on the obtained results in testing (Anon., a). MATERIALS AND METHODS The 9 participant laboratories received each a set with 6 bovine sera: with positive (E, E), doubtful (E, E) and negative (E, E6) results. The samples were analysed by ELISA (Enyzme-linked immunosorbent assay) with absorption step. Each sample had to be worked for 8 times on the same plate, in the same day and the average of the 8 results was considered the final result. The interpretation of results was made according to the criteria established by the kit producer and statistical analyses were made after the reference models described by ISO/IEC GUIDE and (Anon., 997a; 997b). Grubbs Test was used for identifying aberrant results and for elimination of laboratories with unsuitable results (Anon., 99). Thus for each laboratory the standard deviation of the results repeatability and coefficient of variation then standard deviation of the reproducibility results and Z - scores were calculated using the result of Immunology Laboratory of IDAH, as a reference value. RESULTS The final report contains comparative results of laboratories (Table, Fig.) and statistic analyses (Table, Fig. ). Table. The synthesis of qualitative interpretation of results samples Number of E Result of reference Results of samples (E, E, E, E, E, E6) No. of laboratories + IDAH () Positive Doubtful Negative E-Doubtful () (6) () E-Doubtful (8) () 8 () E-Positive 7 (9) () () E-Positive 8 (9) () () E-Negative () () 9 (98) E6-Negative () () 9 (98)

2 Proceedings of 9ICP E E E E E E6 POSITIVE DOUBTFUL NEGATIVE Fig.. Distribution of qualitative results of samples E to E6 Table. The synthesis of CV expressed in qualifying terms Number of E Result of reference Qualifying terms /coefficients of variation No. of laboratories + IDAH () Very well.-6. Well 6. Unsatisfactory > E-Doubtful () (8) (8) E-Doubtful () 8 () () E-Positive () 8 () () E-Positive (8) 6 () () E-Negative () (6) () E6-Negative () () () Mean () () (7) E E E E E E6 Very well Well Unsatisfactory Fig.. Distributions of coefficients of variation The results of Z scores ( Z : satisfactory, < Z : questionable and Z >: unsatisfactory) results were presented in diagrams (Figs.,,, 6, 7, 8) IDAH I DAH The code of l abor at or ies Fig.. Distribution of Z-score values of participating laboratories for sample E. Fig.. Distribution of Z-score values of participating laboratories for sample E

3 Proceedings of 9ICP IDAH I DAH Fig.. Distribution of Z-score values of participating laboratories for sample E Fig. 6. Distribution of Z-score values of participating laboratories for sample E IDAH Fig. 7. Distribution of Z-score values of participating laboratories for sample E I DAH 6 Fig. 8. Distribution of Z-score values of participating laboratories for sample E6 8 9 The sum of Z - scores (Fig. 9) was used for the classification of laboratories which had the same result at the quality interpretation test. Finally, a correlation between the obtained results of Z scores and those of qualitative interpretation was made. Thus the correlation for negative samples E and E6 was, for positive samples E of 97., and E of 9, and for doubtful samples it was as follows: E: 78 and E: (Fig.). Based on the results obtained, laboratories had a satisfactory result, 6 had questionable results and had unsatisfactory results (Fig.) T h e s u m o f Z - s c o r e Fig. 9. Classification of laboratories according to sum of Z-scores

4 Proceedings of 9ICP Fig.. Diagram based on evaluation of laboratories after qualitative interpretation of results of all samples. E6 E E E E E E E E E E E6 6 8 Fig.. Correlation between obtained results of Z-score and qualitative interpretation interpretation sum Z - score Fig.. Classification of laboratories after qualitative interpretation of the test and the sum of Z score at the proficiency testing DISCUSSION AND CONCLUSIONS Thirty seven laboratories (9) of the participating laboratories used ELISA kits made by the same producer within the same series, which showed uniformity in the use of reagents, and which in the current case reduced the batch variation.

5 Proceedings of 9ICP - 7 After the qualitative interpretation of ELISA, the following results were correctly identified: E and E6 (negative): 98; E (positive): 9, E (positive): 9, E (doubtful): 6, E (doubtful):. The highest number of doubtful results, 6 for E and 9 for E, were recorded for the samples which had doubtful results. The result of these samples may be elucidated if the laboratory has calculated extended measurement uncertainty. The results showed that a classification as Very well regarding coefficients of variation (CV) were obtained on samples that came from E ( laboratories) and E ( laboratories) for sera with a high concentration of antibodies. The correlation of Z - scores with the results obtained after the interpretation of the qualitative test, leads us to the conclusion that, when sera have a constant homogeneity and high constancy as in case of positive and negative samples, the differences between the two criteria of estimation were insignificant. The interpretation of the results at 9 certainty of the test together with statistic analyses (coefficient of variation, Z - scores) permitted a more efficient evaluation of laboratories. REFERENCES Anon., 997a. ISO/IEC Guide Proficiency testing by interlaboratory comparisons Part : Development and operation of proficiency testing schemes, edition, 997. Anon., 997b. ISO/IEC Guide Proficiency testing by interlaboratory comparisons Part : Selection and use of proficiency testing schemes by laboratory accreditation bodies, edition, 997. Anon., a. Manual of Diagnostic Tests and Vaccines and Terrestrial Animals, th edition,, Chapter... Principles of Validation of Diagnostic assays for infectious diseases. Anon., b. Manual of Diagnostic Tests and Vaccines and Terrestrial Animals, th edition,. Chapter..6. Paratuberculosis ( Johne's disease). Anon., 99. The international harmonized protocol for the proficiency testing of (chemical) analyticaxl laboratories, Pure & Appl Chem, 9,. 6