How is gastroparesis diagnosed?

Gastroparesis Dx. The 'gold standard' is a radiology study called a 'gastric emptying study'. That being said, certain conditions identified during upper endoscopy can be diagnostic. For example a large bezoar - a mass of undigested food (typically) is usually diagnostic.
Nuclear Medicine... Usually diagnosis is performed by gastric emptying study in the nuclear medicine department. A standard solid meal which is radiolabeled with technetium sulfur colloid is ingested and then imaging is performed at certain time points. A percent gastric emptying is then calculated and compared to a database to determine if emptying is abnormal and the degree of abnormality.