Methods and compositions are provided for evaluating a diabetic patient for treatment with an incretin-based therapy. In certain embodiments, evaluation is ongoing and the patient is evaluated at multiple times. In additional embodiments, a diabetic patient is treated with an incretin-based therapy after the patient has been evaluated for expression levels of GLP-1R in a biological sample. In some aspects, the biological sample is specifically a blood sample that has been enriched for peripheral blood monocytes.