Presented here are methods using alpha-methylglucoside (AMG) in vivo as an indicator for glucose absorption from the gastrointestinal (GI) system or glucose excretion in the urine after oral administration of AMG. The methods find use in, for example, but not limited to, determining the effect of a sodium-dependent glucose transporter (SGLT) inhibitor in an animal, comparing the differences in the effects of a first and second SGLT inhibitor in an animal, and diagnosing a disease associated with glucose absorption from the gastrointestinal (GI) system or glucose excretion from the kidney in an animal.