Effect of ELISA kit manufacturing process and incubation time on progesterone concentration measured in dog serum for ovulation diagnosis – Short communication

Abstract

Twenty-two serum samples of healthy bitches were tested with the frozen and lyophilised version of the same ELISA kit (Quanticheck, Faculty of Veterinary Science, Budapest, Hungary). Samples were chosen on the basis of their progesterone (P4) concentrations, which were between 1.00 and 20.00 ng/mL. As it is well known, this range has the highest clinical relevance in ovulation diagnosis. Both types of microplates were read at 15-min intervals from the 15th until the 90th minute (min) of incubation, and the results were compared with those of frozen plates at 60 min of incubation as 100 percent. Lyophilised microplates gave on average 18 percent higher results than the frozen version at equal incubation times. The highest difference between lyophilised and frozen samples was observed at 45 and 60 min of incubation. Ninety-four percent of the reaction in the frozen microplate occurred in the first 15 min, and during the subsequent 30 min the reaction seemingly stopped. After the 45th min of incubation, this 94 percent increased to 108 percent in the subsequent 30 min, which remained the final approximate result at the end of the 90 min of incubation. In contrast to the frozen microplate, the measured concentration increased continuously in the lyophilised version and reached the highest level at the 60th min. The results of the lyophilised microplate reached the same level at 30 min of incubation as those of the frozen version at 60 min. In conclusion, a mechanical increase or decrease of the incubation time does not generate a linear change in the test results. This study demonstrated that the results of a series of samples collected from the same bitch cannot be compared if they are measured with different laboratory methods or different ELISA kits.