Diagnostic Procedures of the Gastrointestinal System
GI System Lab Tests
A blood test to evaluate stomach problems is the gastrin test. This test measures gastric acid secretion or Helicobacter pylori, which is an infection found in peptic ulcer disease.
Blood tests for amylase, lipase, and calcium evaluate the pancreas function.
Total bilirubin and alkaline phosphatase evaluate the biliary system.
The function of the intestine can be evaluated with total protein, D-Xylose absorption test, and lactose intolerance test.
Urine tests to evaluate GI function include urine bilirubin, urobilinogen, and urine amylase.
Stool can be collected and examined for occult (hidden) blood, bacteria, fat content, and ova, and parasites. The stool culture checks for abnormal bacteria in the digestive tract that may cause diarrhea or other problems.
Fecal Occult Blood Test
The fecal occult blood test checks for occult blood in the stool that is useful in identifying bleeding in the GI tract. A guaiac smear test is used, which involves placing a small amount of stool on a card of guaiac paper and applying hydrogen peroxide, which turns the paper blue if it is positive for blood.
GI System Imaging Tests
There are several imaging tests that can be done to evaluate the GI system.
The GI tract may be visualized by doing a barium swallow or barium enema. Barium is a radiopaque substance that outlines the passageways of the GI tract for viewing by x-ray or fluoroscopy.
The barium swallow is also called an upper GI series, as it examines the upper part of the digestive system—the esophagus, stomach, and duodenum. It allows for examination of the structure, position, peristaltic activity, and motility of the organs. It helps to detect ulcers, hiatal hernias, tumors, abnormal anatomy, malposition, or inflammation.
The upper GI series involves swallowing barium (the contrast medium), in a milkshake form; however, it tastes unpleasant and may cause vomiting. The test takes about 45 minutes, in which x-rays are taken at various intervals. The nurse needs to ensure the patient is NPO for at least 6 hours before the test.
Then, following the test, the patient is given a laxative to quicken the elimination of the barium.
A lower GI series, or barium enema, is done to examine the rectum, large intestine, and the lower part of the small intestine. It is used to detect colon polyps, tumors, and chronic inflammatory bowel disease.
Prior to the procedure, the patient must cleanse the bowel with laxatives and/or enemas. They may also need to follow a liquid diet for 24 hours before the test, and then remain NPO for 8 hours prior to the test.
The procedure requires about 30 minutes, while the patient is placed in various positions as a radiologist observes the barium flowing through the colon on a monitor.
Following the test, laxatives are given to expedite the removal of the barium.
Ultrasonography is another diagnostic imaging technique in which high-frequency sound waves are transmitted into the abdomen, creating echoes that vary with tissue density. The transducer wand placed on the skin sends sound waves into the body that bounce off organs and are electronically converted into computer images. Ultrasounds reveal organ size, shape, and position and can assist in diagnosing cysts, tumors, and stones.
The patient should remain NPO for 8 to 12 hours prior to the test, since gas in the bowel may interfere with results. It is often the preferred procedure, especially for diagnosing gallbladder disease, since it does not expose the patient to radiation and it is painless and safe.
Computed Tomography (CT)
Computed Tomography (CT) is an imaging test that uses multiple x-rays to make detailed images of the body. A computer then reconstructs the data into two-dimensional images to show details of bones, muscles, fat, and organs. The CT scan can be used to assess patients with gallbladder, biliary ductal system, or pancreatic problems. CT angiography combines a CT scan with the injection of contrast media to emphasize differences in tissue density in the pancreas and better visualize the biliary tract.
The patient should be assessed for allergies to iodine, seafood, or contrast medium and remain NPO for 8 to 12 hours before the test. There are no specific aftercare instructions.
Magnetic resonance imaging (MRI)
Magnetic resonance imaging (MRI) is a diagnostic test that uses strong magnetic fields, radio frequencies, and a computer to generate detailed images of organs, soft tissues, bone, and all other structures within the body. The test is painless and does not involve x-rays; however, due to the requirement to lie still in the tunnel-like machine, patients that are claustrophobic or unable to hold still may need a sedative to help them relax.
It is important that all metal objects, such as jewelry and wheelchairs be removed from the MRI room. Patients with pacemakers, metal clips, or rods in the body cannot have an MRI done.
In GI nuclear scanning, a small amount of radioactive material is introduced into the body and a special camera is used to detect the radioactivity, producing images of the GI tract that can’t be seen as well with standard x-rays.
There are five types of GI nuclear scans. The radioactive material is injected into a vein for the GI bleeding scan, liver-spleen scan, and gallbladder nuclear scan. Radioactive material is ingested orally for the gastroesophageal reflux scan and gastric emptying scan.
These tests are valuable for detecting gallbladder disease, tumors, GI bleeding, liver function and abnormalities, and other digestive disorders.
Cholangiography involves the x-ray examination of the bile ducts using a contrast medium to locate and identify stones, strictures, or tumors. The radiopaque dye may be administered by IV or injected directly into the common bile duct.
The patient remains NPO for 8 hours before the test and typically rests in bed about 6 hours after the test.
Endoscopy procedures allow for direct visualization of portions of the GI tract by using a long, flexible, fiberoptic scope. Endoscopy means looking inside, in which an endoscope is inserted directly into the organ and images from the camera tip are seen on a video screen. It may be used for inspection, biopsy, removal of polyps and stones, and to control GI bleeding with laser, photocoagulation, or sclerosing agents.
Most endoscopic procedures are performed on an outpatient basis.
Upper GI Endoscopy
An upper GI endoscopy may look at just the esophagus (an esophagoscopy), the stomach (gastroscopy), or the duodenum (duodenoscopy). If it involves the entire region, it is called an esophagogastroduodenoscopy (more easily referred to as an EGD). This test is useful for identifying the source of upper GI bleeding and for determining whether there is a gastric malignancy or benign ulcer. It can also differentiate between gastric ulcers and duodenal ulcers.
An EGD can visualize esophageal strictures, varices, tumors, hiatal hernias, and achalasia, as well as surgically remove gastric polyps. To prepare for an EGD, the nurse instructs the patient to remain NPO for 8 hours prior to the test. The test usually lasts 15-30 minutes and involves introducing air into the stomach to improve visibility, causing the patient to feel pressure or fullness. Following the procedure, the nurse monitors the patient’s vital signs every 30 minutes for 3 to 4 hours, while also monitoring for signs of pain, bleeding, dyspnea (difficulty breathing), or acute dysphagia (difficulty swallowing).
Endoscopic Retrograde Cholangiopancreatography (ERCP)
Another test involving the oral insertion of an endoscope is the endoscopic retrograde cholangiopancreatography (ERCP). This test is used to identify stones, tumors, or narrowing in the biliary and pancreatic ducts.
Once the endoscope is properly placed, contrast agent can be injected through the ducts, which is visible on x-rays. If needed, a biopsy can be taken, a gallstone can be removed, or a stent can be placed in a narrowed bile duct. An ERCP is an outpatient procedure that usually takes about 30 to 60 minutes, then the patient goes to recovery for 1 to 2 hours. The risks of ERCP include pancreatitis, intestinal perforation, and bleeding.
Magnetic Resonance Cholangiopancreatography (MRCP)
Another technique used to look at the gallbladder, biliary ducts, and pancreatic duct, is the magnetic resonance cholangiopancreatography (MRCP). However, it is a non-invasive procedure that uses magnetic resonance imaging to see if gallstones are lodged in any ducts surrounding the gallbladder.
A colonoscopy is an endoscopic procedure that allows for the examination of the entire colon. It is used to help identify malignant growths, take biopsy specimens, remove polyps, and locate bleeding.
Preparation for the test involves a 1-day thorough bowel cleansing with an oral osmotic solution, in which 8 ounces are taken every 15 minutes to induce profuse diarrhea that lasts about 4 hours. Patients are sedated before the colonoscopy.
As the colonoscope is inserted through the rectum up into the colon, air is introduced to allow for better visualization. The procedure lasts 20 to 60 minutes and the nurse should monitor the patient for full recovery from the sedation. Any changes in vital signs or the development of fever, rectal bleeding, or severe abdominal pain should be reported to the physician immediately.
A sigmoidoscopy is similar to a colonoscopy, but it only allows for the visualization of the anus, rectum, and distal sigmoid colon. It is helpful in identifying the causes of abdominal pain, constipation, diarrhea, bleeding, and abnormal growths. The cost is considerably less than a colonoscopy, but sedation is not usually used and it is uncomfortable for the patient.
Most doctors recommend a colonoscopy as the best test for colon cancer screening. It should be done every 10 years, starting at the age of 50.
A lot of the digestive tract can be seen using upper endoscopy or colonoscopy, but it is harder to see the small intestine.
Capsule endoscopy is one way to visualize the small intestine, in which the patient swallows a capsule containing a light source and tiny camera. The capsule travels through the stomach and small intestines, which usually takes about 8 hours, taking thousands of pictures as it travels. The pictures are sent to a device worn around the patient’s waist, and can then be downloaded to a computer for the doctor to view as a video. The capsule passes out of the body during a normal bowel movement.
This method can be used to find the source of pain, bleeding, or other symptoms in the small intestine; however, it is not useful for looking closely at the colon and it is expensive.
Virtual colonoscopy is a fairly new procedure that is really not an endoscopy procedure, but an imaging test. It uses a CT scan to create a 3-D picture that looks at the inside surfaces of the colon. The images can even be used to create a moving ‘fly-through view on the screen, much like an actual colonoscopy.
The advantage to this type of test is that no drugs are needed and it is totally noninvasive. It shows good detail; however, it doesn’t show the fine surface detail seen in a standard colonoscopy. If something abnormal is found, the patient may still need a standard colonoscopy to get better pictures, take biopsy samples, or remove growths.
There are several other diagnostic tests that may be used to evaluate abnormal function of the esophagus. While endoscopy can look at the lining of the esophagus, it does not usually provide information about the cause of the problem. Three major symptoms to evaluate include difficulty swallowing (dysphagia), heartburn, and chest pain. There are three basic tests used to assess esophageal function: manometry, esophageal pH monitoring, and x-ray studies. We discussed x-ray studies earlier, with the barium swallow and radionuclide scanning.
Manometry is a test that measures the pressure changes in the lower esophageal sphincter and records the sequence and duration of peristaltic movements within the esophagus, with the patient at rest and during swallowing. The patient swallows a small tube that senses changes in pressures in the esophagus.
This test is useful for investigating dysphagia and identifying diseases that produce disturbances of motility or contractions of the esophagus.
Esophageal pH Monitoring Test
To evaluate recurrent heartburn or GERD, esophageal pH monitoring tests for the esophagus’ exposure to acid reflux from the stomach over a 24-hour period. A thin tube with a pH monitor is swallowed and stays in the esophagus to record changes in acidity, while the patient also documents their symptoms during specific activities.
In conjunction with manometry and pH monitoring, the doctor may also perform an acid clearing test and a Bernstein test (acid perfusion test).
In the acid clearing test, hydrochloric acid is directed into the esophagus and if the patient has to swallow more than 10 times to move the acid down, there is a problem with esophageal motility.
In the Bernstein test, a small amount of hydrochloric acid is also directed into the esophagus, and if the patient feels pain from the acid, the test is positive for reflux esophagitis. No pain means another explanation must be sought for the patient’s heartburn symptoms.
Gastric Function Tests
Gastric function tests, such as gastric analysis, examine the gastric acid in the stomach when fasting and when stimulated. Abnormal secretion of acid may be related to a gastric disease, such as ulcers, pernicious anemia, malignancy, or Zollinger-Ellison syndrome.
This concludes our tutorial on GI diagnostic procedures. I hope this overview of lab tests, imaging, and endoscopic procedures is helpful!