If a peptic ulcer perforates, air will leak from inside the gastrointestinal tract (which always contains some air) to the peritoneal cavity (which normally never contains air). This leads to "free gas" within the peritoneal cavity. If the person stands, as when having a chest X-ray, the gas will float to a position underneath the diaphragm. Therefore, gas in the peritoneal cavity, shown on an erect chest X-ray or supine lateral abdominal X-ray, is an omen of perforated peptic ulcer disease. Classification
Peptic ulcers are a form of acid–peptic disorder. Peptic ulcers can be classified according to their location and other factors. By location
Duodenum (called duodenal ulcer)
Esophagus (called esophageal ulcer)
Stomach (called gastric ulcer)
Meckels diverticulum (called Meckels diverticulum ulcer; is very tender with palpation)

Modified Johnson
Type I: Ulcer along the body of the stomach, most often along the lesser curve at incisura angularis along the locus minoris resistantiae. Not associated with acid hypersecretion. Type II: Ulcer in the body in combination with duodenal ulcers. Associated with acid oversecretion. Type III: In the pyloric channel within 3 cm of pylorus. Associated with acid oversecretion. Type IV: Proximal gastroesophageal ulcer. Type V: Can occur throughout the stomach. Associated with the chronic use of NSAIDs (such as ibuprofen). Macroscopic appearance
Gastric ulcers are most often localized on the lesser curvature of the stomach. The ulcer is a round to oval parietal defect ("hole"), 2–4 cm diameter, with a smooth base and perpendicular borders.
Additionally, a false negative result is possible with a blood test if the person has recently been taking certain drugs, such as antibiotics or proton-pump inhibitors.The diagnosis of Helicobacter pylori can be made by:

Urea breath test (noninvasive and does not require EGD);
Direct culture from an EGD biopsy specimen; this is difficult and can be expensive. Most labs are not set up to perform H. pylori cultures;
Direct detection of urease activity in a biopsy specimen by rapid urease test;
Measurement of antibody levels in the blood (does not require EGD). It is still somewhat controversial whether a positive antibody without EGD is enough to warrant eradication therapy;
Stool antigen test;
Histological examination and staining of an EGD biopsy.The breath test uses radioactive carbon to detect H. pylori. To perform this exam, the person is asked to drink a tasteless liquid that contains the carbon as part of the substance that the bacteria breaks down. After an hour, the person is asked to blow into a sealed bag. If the person is infected with H. pylori, the breath sample will contain radioactive carbon dioxide. This test provides the advantage of being able to monitor the response to treatment used to kill the bacteria. The possibility of other causes of ulcers, notably malignancy (gastric cancer), needs to be kept in mind. This is especially true in ulcers of the greater (large) curvature of the stomach; most are also a consequence of chronic H. pylori infection.