Effects of storage time on stability of salivary immunoglobulin A and lysozyme

BACKGROUND: In many research settings, storage of samples prior to analysis is unavoidable. This study investigates the effects of storage time on stability of salivary immunoglobulin A (IgA) and lysozyme. METHODS: Saliva samples were obtained from 30 healthy adults. Each sample was divided into five aliquots and stored at -30 degrees C until analysis. The samples were measured for IgA and lysozyme concentrations after 1, 2, 3, 8 and 12 months of storage using enzyme-linked immunosorbent assay. RESULTS: There was a decline in the concentrations of IgA and lysozyme with increasing storage time. Repeated measures analyses for both salivary IgA and lysozyme showed a significant difference after 8 months of storage as compared to the 1st month (p<0.05). IgA levels decreased significantly with % change in majority of the samples >10% after storage for 8 months or more. A similar pattern was observed for lysozyme with % change in majority of the samples >14% levels when the samples were assayed at 8th month and beyond (mean% change+/-S.D.>14%). CONCLUSION: Salivary IgA and lysozyme concentrations remain stable for up to 3 months when stored at -30 degrees C. These findings have important implications with regard to measurement validity of salivary biomarkers research.