A method of sample analysis is provided. In certain embodiments, the method comprises: a) labeling cells of a blood sample using an antibody that specifically binds to phospho-AMPK or a phosphorylated target thereof, to produce a labeled sample; and b) measuring antibody binding by a population of blood cells of the labeled sample using flow cytometry. In particular embodiments, the method may further comprise, prior to the labeling step: contacting blood with a test agent ex vivo or in vivo; and comparing the evaluation to results obtained from a reference sample of blood cells.