The Immunology Department from Institute for Diagnosis and Animal Health has organized a paratuberculosis serological diagnosis capacity testing through proficiency testing by interlaboratory comparisons of veterinary laboratories from 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. The 39 participant laboratories received each a set with 6 bovine sera: 2 with positive (E3, E4), 2 doubtful, (E1, E2) and 2 negative (E5, E6) results.

The samples were analysed by ELISA (Enyzme-linked immunosorbent assay) with absorption step. In accordance with the instructions 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 was made according to the criteria established by the kit producer.

The final report contains comparative results of laboratories and statistic analyses which were made according to the reference models described by ISO/IEC GUIDE 43-1 and 43-2. Thus for each laboratory the standard deviation of the results repeatability and variation coefficient, then standard deviation of the reproducibility results and Z - scores were calculated using the result of Immunology Laboratory of IDAH, as a reference value. Grubbs test was used for identifying aberrant results and for elimination of laboratories with unsuitable results.

The results of Z-scores were presented in diagrams. In the end it was made a correlation between the obtained results of Z - scores and those of qualitative interpretation. Thus the correlation for negative samples E5 and E6 was 100%, for positive samples E4 of 95%, and E3 of 97,5% and for doubtful samples was as follows: E1 77,5% and E2-52,5%.

The sum of Z scores was used for the classification of laboratories which had the same result at the quality interpretation test. Following the results obtained, 31 laboratories obtained satisfactory result, 6 questionable and 2 unsatisfactory.

The statistical analyses together with the results of the test permitted a better evaluation of laboratories.

Key words: paratuberculosis, ELISA, score Z, proficiency testing