Comparison of OPN ELISA tests. A) Our assay was tested for quantification of recombinant fl-OPN using monoclonal antibodies 2F10 and 1F11-biotin. 2F10 reacts to an epitope on the N-terminal of human OPN and 1F11-biotin reacts with an epitope on the C-terminal side of human OPN. The optical density of the color product is proportional to the quantity of human OPN. The measuring range is from 78 pg/ml to 10 ng/ml. B) Commercially prepared human OPN standards of high (10.1 ng/ml-13.1 ng/ml), medium (5 ng/ml-6.6 ng/ml) or low (1.7 ng/ml-2.3 ng/ml) concentrations were used in four ELISA tests: our in-house test, and those commercially available from Assay Designs, R&D Systems (Quantikine) and IBL. The IBL results are graphed separately because the IBL quantification yielded values that were extremely high compared to the other assays and the standard ranges.