STABILITY OF AN ELISA TEST SYSTEM BASED ON A RECOMBINANT CHIMERIC SM PROTEIN FOR THE DETECTION OF ANTIBODIES TO SARS-COV-2 UNDER DIFFERENT TEMPERATURE CONDITIONS

Assessment of the stability of kit components is a critical step in the development of enzyme-linked immunosorbent assay (ELISA) systems, as it directly determines the accuracy and reproducibility of diagnostic results during storage and routine use. In the present study, the stability and reproducibility of a newly developed ELISA test system based on the recombinant chimeric SM protein were evaluated under different temperature conditions. The stability of the kit components was assessed by monitoring changes in the analytical signal, expressed as optical density (OD), and the variability of replicate measurements, expressed as the coefficient of variation (CV, %), over a controlled period at -20ºC, 4ºC, 22ºC, and 37ºC. The results demonstrated that the stability of the developed ELISA test system was strongly temperature-dependent. Standard refrigerated storage at 4ºC was identified as the optimal condition, providing the highest preservation of the analytical signal, with 81.3% of the initial signal retained (OD₄₅₀ = 1.933), while maintaining high reproducibility (CV = 1.74%), consistently below the predefined acceptance threshold of ≤5%. Storage at -20ºC showed notable limitations. Despite maintaining a relatively high analytical signal (OD₄₅₀ = 1.623) and 68.2% residual activity, freezing and thawing of the reagents resulted in increased analytical variability (CV = 5.56%), exceeding the established acceptance criterion. Exposure to elevated temperatures of 22ºC and 37ºC had a pronounced detrimental effect on test-system stability, resulting in degradation of protein components and a loss of more than 65% of the initial activity. These findings demonstrate that, to ensure long-term preservation of the sensitivity, specificity, and reproducibility of the developed ELISA diagnostic kit, storage at 4ºC under properly maintained cold-chain conditions is an essential technological requirement.