Final answer:
An Esophagogastroduodenoscopy (EGD) is the initial diagnostic test for gastritis, using an endoscope to examine the upper GI tract and possibly take tissue samples for biopsy.
Step-by-step explanation:
An Esophagogastroduodenoscopy (EGD) via an endoscope with biopsy is the initial diagnostic test for gastritis. This medical procedure involves using an endoscope to look inside the esophagus, stomach, and duodenum to identify any potential issues such as inflammation, ulcers, or tumors. Small tissue samples can be taken for biopsy to confirm gastritis or other conditions. The endoscope is a flexible tube with a light and camera attached, allowing doctors to examine the upper gastrointestinal (GI) tract and obtain images. EGD is not used for diagnosing diabetes, treating gallstones, or screening for colon cancer.