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Purpose and Limits of Adjustment of A Discrimination Level in Fossomatic-90 Apparatuses

RYSANEK D, BABAK V, SLEHOFEROVA L
Veterinarni Medicina 39, 1994, 45-54

The purpose and limits of adjustment of a discrimination level were investigated in four Fossomatic 90 apparatuses (manufactured by A/S N. Foss Electric, Denmark) using six bulk milk samples with the range of somatic cell counts (SCC hereinafter) 203 to 728.10(3)/ml and in a Fossomatic 250 apparatus, with regard to agreement with the results of a reference direct microscopic method. We recommend to introduce a nation ''the level of real discrimination'', i.e. the lowest adjustment of a discriminator in which the number of parasitic impulses determined by measuring blank samples does not exceed the value of 5,000 per ml. We regard the adjustment of discrimination level below this value in order to approximate the results of determination to the values of a reference direct microscopic method is unfair in keeping with the manufacturer's recommendation. We should also be aware of the fact that the value of actual discrimination is specific for each Fossomatic 90 apparatus (Fig. 1). Hence it is not possible to recommend ''an optimum level of discrimination'' which would be valid in general. A graphical analysis of the cumulative values of SCC on different values of discrimination level that it is not possible to use this procedure for determination of an optimum discrimination level (Figs. 2 to 5). It would not be realistic to ''calibrate'' the Fossomatic 90 apparatuses by means of regression of the SCC values determined on the apparatus on the values of the reference direct microscopic method. It has been demonstrated than in some apparatuses the change in discrimination adjustment cannot show a statistically insignificant difference from the values of the reference direct microscopic method as a statistically significant difference was read even for the adjustment of real discrimination level (Tab. I). In such apparatuses this situation, especially if it is confirmed that the admissible tolerance of critical values in a collaborative trial has been exceeded, should be a signal to call a technician to repair this apparatus. It is not advisable to insist on the certified value of discrimination stated by the manufacturer of the Fossomatic 90 apparatus. In some cases, a change in the adjustment of discrimination level can show a statistically insignificant difference between SCC determined by die apparatus and the values of the reference direct microscopic method. This applies particularly to the apparatuses indicating a positive, statistically significant difference from the reference direct microscopic method (Tab. II, apparatus no. 4). But this procedure is not generally applicable as documented by the presented results


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