Canadian Immunohistochemistry Quality Control (CIQC) operates an academic proficiency testing (PT) program using a traditional expert panel-based qualitative assessment system. The image analysis approach is increasingly considered for use in PT to follow demand for precision in immunohistochemical test calibration. CIQC introduces and explores the usefulness of a novel image analysis-based tool, the laboratory score/reference method score ratio (LSRSR) for PT. Two CIQC runs with 33 and 57 participants, respectively, were analyzed for interlaboratory concordance for estrogen receptor results using expert panel-based and LSRSR systems. Samples included tissue microarrays with 40 tissue cores each. The LSRSR was calculated from participants' and reference laboratory H scores measured by image analysis. We found lower concordance with reference method results for participating laboratories by LSRSR than those reported by the expert panel; although the expert panel observed those differences, it was not able to measure them without LSRSR. LSRSR may be useful in monitoring laboratory performance for quantitative immunohistochemical testing.