The relationship between total tear protein concentrations determined by different methods and standards

Background: It is known that the values of total protein concentration (TPC ) of human tears obtained by different methods/standards vary considerably. The variations are due to differences in reactivity of proteins to the met hods used. The aim of this study was to investigate the relationships and a greements between TPC values obtained by different methods/standards. Metho ds: Two experiments were conducted. In experiment 1, 30 normal subjects wer e recruited and their TPC were determined by the Bradford and the modified Lowry methods, with bovine serum albumin and bovine immunoglobulin G as sta ndards. The relationships (equations) between TPC values obtained by differ ent methods/standards were determined. In experiment 2, another 15 normal s ubjects were recruited and the TPC were measured as in experiment 1. Measur ed values of TPC using different methods/standards were compared with their respective values calculated from the equations defined in experiment 1. T he agree ment and the reliability between the measured and the calculated v alues were investigated. Results: Experiment 1 showed that the TPC obtained by different methods/standards were strongly correlated to one another, an d their relationships can be defined by linear equations. In experiment 2, the measured and the calculated values, using the equations defined in expe riment 1, showed good agreement and reliability. This indicates that TPC ob tained by one method/standard can be used to estimate the value(s) that wou ld be obtained if another method/standard were used using the equation(s) f ound in experiment 1. Conclusion: The correlations between TPC values obtai ned by different methods/standards were strong. Our results also indicated good agree ment and reliability between measured and calculated TPC values. Therefore, values obtained by different methods/standards are interchangea ble using the appropriate equations.