We demonstrate a three-step assay on a silicon photonic microring resonator-based detection platform that enables the quantitation of the cardiac biomarker C-reactive protein (CRP) over a dynamic range spanning six orders of magnitude. Using antibody-modified microrings, we sequentially monitor primary CRP binding, secondary recognition of bound CRP by a biotinylated antibody, and tertiary signal amplification using streptavidin-functionalized beads. This detection methodology is applied to CRP quantitation in human serum and plasma samples.