Gastroscopy, or endoscopic evaluation of the stomach, is useful in chronic cases of colic suspected to be caused by gastric ulcers, gastric impactions, and gastric masses. A 3-meter scope is required to visualize the stomach of most horses, and the horse must be fasted prior to scoping.

Laparoscopy involves inserting a telescoping camera approximately 1 cm in diameter into the horse's abdomen, through a small incision, to visualize the gastrointestinal tract. It may be performed standing or under general anesthesia, and is less invasive than an exploratory celiotomy (abdominal exploratory surgery).

A diagnosis of gastric dilatation-volvulus is made by several factors. The breed and history will often give a significant suspicion of gastric dilatation-volvulus, and the physical exam will often reveal the telltale sign of a distended abdomen with abdominal tympany. Shock is diagnosed by the presence of pale mucous membranes with poor capillary refill, increased heart rate, and poor pulse quality. Radiographs (x-rays), usually taken after decompression of the stomach if the dog is unstable, will show a stomach distended with gas. The pylorus, which normally is ventral and to the right of the body of the stomach, will be cranial to the body of the stomach and left of the midline, often separated on the x-ray by soft tissue and giving the appearance of a separate gas filled pocket (double bubble sign).

On chest radiography, a retrocardiac, gas-filled viscus may be seen in cases of intrathoracic stomach, which confirms the diagnosis. Plain abdominal radiography reveals a massively distended viscus in the upper abdomen. In organoaxial volvulus, plain films may show a horizontally oriented stomach with a single air-fluid level and a paucity of distal gas. In mesenteroaxial volvulus, plain abdominal radiographic findings include a spherical stomach on supine images and 2 air-fluid levels on erect images, with the antrum positioned superior to the fundus.

- Upper GI contrast studies:

The diagnosis of gastric volvulus is usually based on barium studies; however, some authors recommend computed tomography (CT) scanning as the imaging modality of choice.

Upper gastrointestinal (GI) contrast radiographic studies (using barium or Gastrografin) are sensitive and specific if performed with the stomach in the "twisted" state and may show an upside-down stomach. Contrast studies have been reported to have a diagnostic yield in 81–84% of patients.

Often performed for an evaluation of acute abdominal pain, a computed tomography (CT) scan can offer immediate diagnosis by showing two bubbles with a transition line. Proponents of CT scanning in the diagnosis of gastric volvulus report several benefits, including:

1. the ability to rapidly diagnose the condition based on a few coronal reconstructed images,

2. the ability to detect the presence or absence of gastric pneumatosis and free air,

3. the detection of predisposing factors (i.e., diaphragmatic or hiatal hernias), and

4. the exclusion of other abdominal pathology.

- Endoscopy:

Upper gastrointestinal (GI) endoscopy may be helpful in the diagnosis of gastric volvulus. When this procedure reveals distortion of the gastric anatomy with difficulty intubating the stomach or pylorus, it can be highly suggestive of gastric volvulus. In the late stage of gastric volvulus, strangulation of the blood supply can result in progressive ischemic ulceration or mucosal fissuring.

The nonoperative mortality rate for gastric volvulus is reportedly as high as 80%. Historically, mortality rates of 30–50% have been reported for acute gastric volvulus, with the major cause of death being strangulation, which can lead to necrosis and perforation. With advances in diagnosis and management, the mortality rate from acute gastric volvulus is 15–20% and that for chronic gastric volvulus is 0–13%.

Immediate treatment is the most important factor in a favorable prognosis. A delay in treatment greater than six hours or the presence of peritonitis, sepsis, hypotension, or disseminated intravascular coagulation are negative prognostic indicators.

Historically, GDV has held a guarded prognosis. Although "early studies showed mortality rates between 33% and 68% for dogs with GDV," studies from 2007 to 2012 "reported mortality rates between 10% and 26.8%". Mortality rates approach 10% to 40% even with treatment. A study determined that with prompt treatment and good preoperative stabilization of the patient, mortality is significantly lessened to 10% overall (in a referral setting). Negative prognostic indicators following surgical intervention include postoperative cardiac arrhythmia, splenectomy, or splenectomy with partial gastric resection. Interestingly, a longer time from presentation to surgery was associated with a lower mortality, presumably because these dogs had received more complete preoperative fluid resuscitation and were thus better cardiovascularly stabilized prior to the procedure.

On x-rays, gas may be visible in the abdominal cavity. Gas is easily visualized on x-ray while the patient is in an upright position. The perforation can often be visualised using computed tomography. White blood cells are often elevated.

The most confirmatory investigation is endoscopy of upper gastrointestinal tract.

Laboratory

- Individuals with gastric outlet obstruction are often hypochloremic, hypokalemic, and alkalotic due to loss of hydrogen chloride and potassium. High urea and creatinine levels may also be observed if the patient is dehydrated.

Abdominal X-ray

- A gastric fluid level may be seen which would support the diagnosis.

Barium meal and follow through

- May show an enlarged stomach and pyloroduodenal stenosis.

Gastroscopy

- May help with cause and can be used therapeutically.

The differential diagnosis of gastric outlet obstruction may include: early gastric carcinoma hiatal hernia, gastroesophageal reflux, adrenal insufficiency, and inborn errors of metabolism.

Surgical intervention is nearly always required in form of exploratory laparotomy and closure of perforation with peritoneal wash. Occasionally they may be managed laparoscopically.

Conservative treatment including intravenous fluids, antibiotics, nasogastric aspiration and bowel rest is indicated only if the person is nontoxic and clinically stable.

Other radiological studies frequently used to assess patients with chronic stomach problems include a barium swallow, where a dye is consumed and pictures of the esophagus and stomach are obtained every few minutes. Other tests include a 24-hour pH study, CT scans or MRI.

The diagnosis of Boerhaave's syndrome is suggested on the plain chest radiography and confirmed by chest CT scan. The initial plain chest radiograph is almost always abnormal in patients with Boerhaave's syndrome and usually reveals mediastinal or free peritoneal air as the initial radiologic manifestation. With cervical esophageal perforations, plain films of the neck show air in the soft tissues of the prevertebral space.

Hours to days later, pleural effusion(s) with or without pneumothorax, widened mediastinum, and subcutaneous emphysema are typically seen. CT scan may show esophageal wall edema and thickening, extraesophageal air, periesophageal fluid with or without gas bubbles, mediastinal widening, and air and fluid in the pleural spaces, retroperitoneum or lesser sac.

The diagnosis of esophageal perforation could also be confirmed by water-soluble contrast esophagram (Gastrografin), which reveals the location and extent of extravasation of contrast material. Although barium is superior in demonstrating small perforations, the spillage of barium sulfate into the mediastinal and pleural cavities can cause an inflammatory response and subsequent fibrosis and is therefore not used as the primary diagnostic study. If, however, the water-soluble study is negative, a barium study should be performed for better definition.

Endoscopy has no role in the diagnosis of spontaneous esophageal perforation. Both the endoscope and insufflation of air can extend the perforation and introduce air into the mediastinum.

Patients may also have a pleural effusion high in amylase (from saliva), low pH, and may contain particles of food.

There are many tools for investigating stomach problems. The most common is endoscopy. This procedure is performed as an outpatient and utilizes a small flexible camera. The procedure does require intravenous sedation and takes about 30–45 minutes; the endoscope is inserted via the mouth and can visualize the entire swallowing tube, stomach and duodenum. The procedure also allows the physician to obtain biopsy samples. In many cases of bleeding, the surgeon can use the endoscope to treat the source of bleeding with laser, clips or other injectable drugs.

With the exception of a few case reports describing survival without surgery, the mortality of untreated Boerhaave syndrome is nearly 100%. Its treatment includes immediate antibiotic therapy to prevent mediastinitis and sepsis, surgical repair of the perforation, and if there is significant fluid loss it should be replaced with IV fluid therapy since oral rehydration is not possible. Even with early surgical intervention (within 24 hours) the risk of death is 25%.

The diagnosis is mainly established based on the characteristic symptoms. Stomach pain is usually the first signal of a peptic ulcer. In some cases, doctors may treat ulcers without diagnosing them with specific tests and observe whether the symptoms resolve, thus indicating that their primary diagnosis was accurate.

More specifically, peptic ulcers erode the muscularis mucosae, at minimum reaching to the level of the submucosa (contrast with erosions, which do not involve the muscularis mucosae).

Confirmation of the diagnosis is made with the help of tests such as endoscopies or barium contrast x-rays. The tests are typically ordered if the symptoms do not resolve after a few weeks of treatment, or when they first appear in a person who is over age 45 or who has other symptoms such as weight loss, because stomach cancer can cause similar symptoms. Also, when severe ulcers resist treatment, particularly if a person has several ulcers or the ulcers are in unusual places, a doctor may suspect an underlying condition that causes the stomach to overproduce acid.

An esophagogastroduodenoscopy (EGD), a form of endoscopy, also known as a gastroscopy, is carried out on people in whom a peptic ulcer is suspected. By direct visual identification, the location and severity of an ulcer can be described. Moreover, if no ulcer is present, EGD can often provide an alternative diagnosis.

One of the reasons that blood tests are not reliable for accurate peptic ulcer diagnosis on their own is their inability to differentiate between past exposure to the bacteria and current infection. 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 to do, 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 will be asked to drink a tasteless liquid which contains the carbon as part of the substance that the bacteria breaks down. After an hour, the person will be asked to blow into a bag that is sealed. 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.

If a peptic ulcer perforates, air will leak from the inside of 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 erect, 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.

The diagnosis of hemosuccus pancreaticus can be difficult to make. Most patients who develop bleeding in the gastrointestinal tract have endoscopic procedures done to visualize the bowel in order to find and treat the source of the bleeding. With hemosuccus, the bleeding is coming from the pancreatic duct which enters into the first part of the small intestine, termed the duodenum. Typical gastroscopes used to visualize the esophagus, stomach and duodenum are designed with fiber-optic illumination that is directed in the same direction as the endoscope, meaning that visualization is in the forward direction. However, the pancreatic duct orifice is located on the side of the duodenum, meaning that it can be missed on forward-viewing endoscopy. A side-viewing endoscope (known as a "duodenoscope", or "side-viewer") used for endoscopic retrograde cholangiopancreatography (ERCP), a procedure to visualize the bile ducts and pancreatic duct on fluoroscopy, can be used to localize the bleeding to the pancreatic duct. It can be confused with bleeding from the common bile duct on endoscopy, leading to the term "pseudohematobilia".

Liver function test is normal apart from an increased serum bilirubin in the event of pancreaticobiliary reflux. Serum amylase is normal outside episodes of acute pancreatitis. It is difficult to diagnose HP because the bleeding is usually intermittent. Endoscopy is essential in ruling out other causes of upper gastrointestinal bleeding and in rare cases; active bleeding can be seen from the duodenal ampulla. Even though endoscopy may be normal, it helps to rule out other causes of upper digestive bleeding (erosive gastritis, peptic ulcers, and oesophageal and gastric fundus varices, etc.). Ultrasonography can be used to visualize pancreatic pseudocysts or aneurysm of the peripancreatic arteries. Doppler ultrasound or dynamic ultrasound has been reported to be diagnostic. Contrast-enhanced CT is an excellent modality for demonstrating the pancreatic pathology and can also demonstrate features of chronic pancreatitis, pseudocysts, and pseudoaneurysms. On precontrast CT, the characteristic finding of clotted blood in the pancreatic duct, known as the sentinel clot, is seldom seen. Computed tomography may show simultaneous opacification of an aneurysmal artery and pseudocyst or persistence of contrast within a pseudocyst after the arterial phase. Again, these findings are only suggestive of the diagnosis. Ultimately, angiography is the diagnostic reference standard. Angiography identifies the causative artery and allows for delineation of the arterial anatomy and therapeutic intervention.

Gastric volvulus or volvulus of stomach is a twisting of all or part of the stomach by more than 180 degrees with obstruction of the flow of material through the stomach, variable loss of blood supply and possible tissue death. The twisting can occur around the long axis of the stomach: this is called organoaxial or around the axis perpendicular to this, called mesenteroaxial. Obstruction is more likely in organoaxial twisting than with mesenteroaxial while the latter is more associated with ischemia. About one third of the cases are associated with a hiatus hernia. Treatment is surgical.

The classic triad (Borchardt's Triad) of gastric volvulus, described by Borchardt in 1904, consists of severe epigastric pain, retching (due to sour taste in mouth) without vomiting, inability to pass a nasogastric tube and reportedly occurs in 70% of cases. Sometimes severe pain at the top of left shoulder, this may be due to internal bleeding irritating the diaphragm upon respiration.

Treatment of hemosuccus pancreaticus depends on the source of the hemorrhage. If the bleeding is identified on angiography to be coming from a vessel that is small enough to occlude, embolization through angiography may stop the bleeding. Both coils in the end-artery and stents across the area of bleeding have been used to control the hemorrhage. However, the bleeding may be refractory to the embolization, which would necessitate surgery to remove the pancreas at the source of hemorrhage. Also, the cause of bleeding may be too diffuse to be treated with embolization (such as with pancreatitis or with pancreatic cancer). This may also require surgical therapy, and usually a distal pancreatectomy, or removal of the part of the pancreas from the area of bleeding to the tail, is required.

Diagnosis of Pancreatic pseudocyst can be based on cyst fluid analysis:

- Carcinoembryonic antigen (CEA) and CEA-125 (low in pseudocysts and elevated in tumors);

- Fluid viscosity (low in pseudocysts and elevated in tumors);

- Amylase (usually high in pseudocysts and low in tumors)

The most useful imaging tools are:

- Ultrasonography – the role of ultrasonography in imaging the pancreas is limited by patient habitus, operator experience and the fact that the pancreas lies behind the stomach (and so a gas-filled stomach will obscure the pancreas).

- Computerized tomography – this is the gold standard for initial assessment and follow-up.

- Magnetic resonance cholangiopancreatography (MRCP) – to establish the relationship of the pseudocyst to the pancreatic ducts, though not routinely used

Incidence of hiatal hernias increases with age; approximately 60% of individuals aged 50 or older have a hiatal hernia. Of these, 9% are symptomatic, depending on the competence of the lower esophageal sphincter (LES). 95% of these are "sliding" hiatus hernias, in which the LES protrudes above the diaphragm along with the stomach, and only 5% are the "rolling" type (paraesophageal), in which the LES remains stationary, but the stomach protrudes above the diaphragm.

Hiatus hernia are most common in North America and Western Europe and rare in rural African communities. Some have proposed that insufficient dietary fiber and the use of a high sitting position for defecation may increase the risk.

Diagnosis of gastric varices is often made at the time of upper endoscopy.

The Sarin classification of gastric varices identifies four different anatomical types of gastric varices, which differ in terms of treatment modalities.

The treatment for bile reflux is the same as the treatment for acidic reflux. In general, everything that can

reduce acidic reflux can reduce bile reflux. Examples include lifestyle modification, weight reduction, and the avoidance of eating immediately before sleep or being in the supine position immediately after meals. In addition, smoking has been found to be a factor in the development of acidic reflux. Thus, all of these factors should be applied to bile reflux as well.

Likewise, drugs that reduce the secretion of gastric acid (e.g., proton pump inhibitors)

or that reduce gastric contents or volume can be used to treat acidic bile reflux. Because prokinetic drugs increase the motility of the stomach and accelerate gastric emptying, they can also reduce bile reflux. Other drugs that reduce the relaxations of the lower esophageal sphincter, such as baclofen, have also proven to reduce bile reflux, particularly in patients who are refractory to (medically unresponsive to) proton pump inhibitor therapy.

Medications used in managing biliary reflux include bile acid sequestrants, particularly cholestyramine, which disrupt the circulation of bile in the digestive tract and sequester bile that would otherwise cause symptoms when refluxed; and prokinetic agents, to move material from the stomach to the small bowel more rapidly and prevent reflux.

Biliary reflux may also be treated surgically, if medications are ineffective or if precancerous tissue is present in the esophagus.

The diagnosis of a hiatus hernia is typically made through an upper GI series, endoscopy or high resolution manometry.

Often, a diagnosis can be made based on the patient's description of their symptoms, but other methods which may be used to verify gastritis include:

- Blood tests:

- Blood cell count

- Presence of "H. pylori"

- Liver, kidney, gallbladder, or pancreas functions

- Urinalysis

- Stool sample, to look for blood in the stool

- X-rays

- ECGs

- Endoscopy, to check for stomach lining inflammation and mucous erosion

- Stomach biopsy, to test for gastritis and other conditions

For practical purposes, gastric pH an endoscopy should be done in someone with suspected achlorhydria. Older testing methods using fluid aspiration through a nasogastric tube can be done, but these procedures can cause significant discomfort and are less efficient ways to obtain a diagnosis.

A complete 24-hour profile of gastric acid secretion is best obtained during an esophageal pH monitoring study.

Achlorhydria may also be documented by measurements of extremely low levels of pepsinogen A (PgA) () in blood serum. The diagnosis may be supported by high serum gastrin levels ().

The "Heidelberg test" is an alternative way to measure stomach acid and diagnose hypochlorhydria/achlorhydria.

A check can exclude deficiencies in iron, calcium, prothrombin time, vitamin B-12, vitamin D, and thiamine. Complete blood count with indices and peripheral smears can be examined to exclude anemia. Elevation of serum folate is suggestive of small bowel bacterial overgrowth. Bacterial folate can be absorbed into the circulation.

Once achlorhydria is confirmed, a hydrogen breath test can check for bacterial overgrowth.

Younger people with ulcer-like symptoms are often treated with antacids or H2 antagonists before endoscopy is undertaken.

People who are taking nonsteroidal anti-inflammatories (NSAIDs) may also be prescribed a prostaglandin analogue (misoprostol) in order to help prevent peptic ulcers.