The measured signals from the two sensor arrays were used to estimate the ratio between the two antigen forms, particularly in the “gray zone” (4 ng/mL < PSA < 10 ng/mL), demonstrating the ability of the system to rapidly distinguish between conditions of PCa or BPH on the basis of the freePSA/total PSA ratio. The gene discussed is KLK3; the disease is posterior cortical atrophy.