Primary care patients aged 50 to 74 years eligible for colorectal cancer screening are randomized to receive a mailed stool blood test kit to complete at home (Control) or to the control condition plus an in-office blood test called GERA that includes assessment of red blood cell folate and DNA-testing for two MTHFR (methylenetetrahydrofolate reductase) single nucleotide polymorphisms (SNPs) (Intervention). The gene discussed is MTHFR; the disease is colorectal cancer.