title: Effects of storage time on stability of salivary immunoglobulin A and lysozyme.
abstract: 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%).
  
  
  CONCLUSIONS
  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.
authors.affiliation: Department of Community, Occupational and Family Medicine, Faculty of Medicine (MD3), National University of Singapore, 16, Medical Drive, Singapore 117597, Singapore.
authors.forename: Vivian
authors.initials: V
authors.lastname: Ng
authors.forename: David
authors.initials: D
authors.lastname: Koh
authors.forename: Qiuyun
authors.initials: Q
authors.lastname: Fu
authors.forename: Sin-Eng
authors.initials: SE
authors.lastname: Chia
mesh_terms: D015415:Biomarkers / Q000032:analysis; D004795:Enzyme Stability; D006801:Humans; D007070:Immunoglobulin A / Q000032:analysis / Q000378:metabolism*; D008297:Male; D009113:Muramidase / Q000032:analysis / Q000378:metabolism*; D015203:Reproducibility of Results; D012463:Saliva / Q000737:chemistry*; D013997:Time Factors
chemical_list: D015415:Biomarkers; D007070:Immunoglobulin A; D009113:Muramidase