Using soybean trypsin inhibitor as an external loading control for Western blot analysis of tear proteins: Application to corneal disease

► Soybean trypsin inhibitor used as external loading control in Western blotting.
► Appropriate for relative protein quantification of biological fluids (e.g. tears).
► High reproducibility with a coefficient of variation <10% was observed.
► Confirmed the presence of secreted frizzled protein 1 (SFRP1) in human tears.
► Relative level of tear SFRP1 was less in keratoconus patients than controls.