|

Tests used in Gastroenterology

Last updated:

Oesophageal Tests

24-hour pH monitoring

This involves passing a catheter through the patient’s nose into the stomach until the tip of an attached pH probe is in the distal oesophagus. The patient wears a small recording unit and pH is recorded for 24 hours.

Oesophageal manometry

This test assesses the motor function of the upper and lower oesophageal sphincters. A catheter is placed through the patient’s nose into the stomach. It is then slowly removed and pressures are recorded. The patient may be asked to take some deep breaths and swallow water.

Stomach Tests

Rapid urease test/urea breath test

The urea breath test can be used to identify the presence of Helicobacter pylori (H. pylori). It works on the ability of H. pylori to convert urea into ammonia and carbon dioxide (CO2). Patients swallow carbon-13 (13C) enriched urea which is converted into ammonia and 13C CO2, which is exhaled. After 30 minutes, the patient exhales into a glass tube and mass spectrometry is used to calculate the amount of 13C CO2 present.

Anti-acid drugs such as proton pump inhibitors should be stopped for at least 2 weeks and antibiotics should be stopped for at least 4 weeks before testing, as these can lead to false negatives.

Upper Gastrointestinal Tract Imaging

Oesophagogastroduodenoscopy (OGD)

Also known as an upper gastrointestinal (GI) endoscopy, this is an endoscopic procedure that visualises the upper GI tract down to the duodenum. It involves passing a narrow flexible tube (gastroscope) down the oesophagus. As well as viewing the GI tract, OGDs can take samples of tissue for biopsy and can be used for therapeutic purposes (e.g. endoscopic band ligation in varices).

Some patients may be offered topical lidocaine to numb the throat or may be offered sedatives (e.g. midazolam) in patients who are anxious or agitated.

Barium swallow

A barium swallow is used to visualise the oesophagus and stomach using a series of x-rays after a patient swallows barium sulfate. Barium sulfate is an insoluble compound and is radiopaque, therefore when consumed, it coats the GI tract which then appears white on an x-ray film.

Lower Gastrointestinal Tract Imaging

Colonoscopy

A colonoscopy is an endoscopic technique which visualises the large bowel and distal small bowel. It involves passing a flexible tube through the anus. Like other endoscopic techniques in the GI tract, it not only visualises tissues but can also be used to take biopsies and be therapeutic.

Around 2 days before a colonoscopy, patients should eat plain foods. 1 day before the colonoscopy, patients are instructed to drink sachets of laxatives to empty their bowels for the test. During the procedure, analgesia and sedation may be offered

Sigmoidoscopy

Unlike a colonoscopy which can visualise the entire colon, a sigmoidoscopy visualises the sigmoid colon. It may be useful over a colonoscopy, for example, in severe ulcerative colitis where a risk of bowel perforation is present, as sigmoidoscopies carry a lower risk of perforation.

Barium enema

Like a barium swallow, barium sulfate is used in barium enemas as it is insoluble and radiopaque. Patients are given laxatives the day before the barium enema to empty their bowels. Serial x-rays are performed and the bowels appear white as they are coated with barium sulfate.

Liver Function Tests

Overview

The term ‘liver function tests (LFTs)’ is a misnomer, as they mainly test the level of damage that has occurred to the liver, rather than its function. They are often also called liver blood tests.

LFTs often include:

Other tests that may be considered are:

Bilirubin

Bilirubin is the resulting product of haem breakdown:

  • Total bilirubin measures both conjugated (direct) and unconjugated indirect) bilirubin
  • Conjugated and unconjugated bilirubin can help to identify where the problem is if there is hyperbilirubinaemia. See Jaundice for more.

Alanine transaminase (ALT) and aspartate transaminase (AST)

Alanine transaminase (ALT) is mostly found in the liver but is also present in the kidneys, muscles, and heart. ALT is found in the cytoplasm of cells, meaning increased levels can suggest cell damage and leakage.

Aspartate transaminase (AST) is less specific than ALT for the liver, as it is mostly found in the mitochondria of cells, and more is present in the kidneys, muscles, and the heart, alongside the liver. Raised AST levels suggest liver, heart, kidney, or muscle damage.

Liver damage is more likely with higher AST and ALT values, with ALT rising more than AST in acute liver damage. Levels >1000 IU/L are strongly suggestive of hepatitis (e.g. drug-induced, viral, autoimmune etc.)

The ratio of AST: ALT can help with identifying the cause:

  • Chronic liver disease: ALT > AST
  • Once cirrhosis occurs: AST > ALT
  • AST: ALT ratio >2 suggests alcoholic liver disease
  • AST:ALT ratio <1 suggests non-alcoholic liver disease
  • Alcoholic liver disease is unlikely to cause an AST >1000 IU/L

Gamma-glutamyltransferase (GGT)

Gamma-glutamyltransferase (GGT) is found in hepatocytes, biliary epithelial cells, the kidneys, and intestines. Key points are:

  • All liver diseases may show increased GGT levels
  • Like ALP, increased GGT levels suggest cholestasis
  • GGT can confirm that a raised ALP is due to liver damage and not another cause

Alkaline phosphatase (ALP)

Alkaline phosphatase (ALP) is an enzyme found in cells lining the bile ducts but also in bone. It is involved in the calcification of bones. Key points are:

  • An elevated ALP (often with elevated GGT) suggests cholestasis
  • A high ALP with normal GGT suggests bone disease

It is important to note that ALP is physiologically increased in pregnancy, and can be as high as 3 times the upper limit of normal.

Albumin

Albumin is a marker of liver function with high sensitivity, as it is made specifically in the liver. Since it has a long half-life, it is not as useful in acute disease. Reduced levels of albumin can cause oedema.

Key points are:

  • Albumin levels can be decreased in chronic liver disease (e.g. cirrhosis)
  • Albumin can also be decreased in nephrotic syndrome, as it is lost through the urine

Isolated increase in bilirubin

Determining whether the bilirubin is conjugated or unconjugated can help with identifying the underlying cause. The causes of an isolated increase in unconjugated bilirubin are:

Conjugated bilirubin levels increase when the liver has lost at least half of its excretory function. Causes may be hepatic or post-hepatic and are discussed in more detail in the Jaundice chapter.

Increased ALT and AST

A rise in AST and ALT greater than ALP and GGT suggests a hepatitic picture. Causes may be:

In general, patients with very high ALT/AST levels are likely to have viral or ischaemic hepatitis or toxic liver injury. Mild increases in ALT/AST are most commonly caused by non-alcoholic fatty liver disease.

Other Liver Tests

Liver biopsy

A liver biopsy may be ultrasound- or CT-guided and involves cleaning the skin over the liver, injecting a local anaesthetic into the overlying skin, and inserting a hollow needle.

Gallbladder and Bile Duct Tests

Endoscopic retrograde cholangiopancreatography (ERCP)

An ERCP is used to diagnose and treat disorders of the bile ducts, gallbladder, pancreas, and liver. Patients may be given local anaesthetic spray to numb the throat and sedatives before the procedure. An endoscope is passed down the oesophagus, through the stomach and pylorus into the duodenum through to the ampulla of Vater (where the common bile duct and pancreatic duct meet).

During an ERCP, a contrast medium may endoscopically be injected into the biliary tree and pancreas, allowing for cholangiopancreatography (x-ray imaging of the bile ducts and pancreas).

An ERCP is both diagnostic and therapeutic. It may be used for gallstone extraction and stent insertion through the ampulla of Vater to allow bile drainage (may be performed in pancreatic cancer for palliation).

An ERCP can carry risks of infection and pancreatitis.

Magnetic resonance cholangiopancreatography (MRCP)

An MRCP is a relatively safer and non-invasive alternative to an ERCP and uses magnetic resonance imaging (MRI) to produce images of the liver, bile ducts, gallbladder, and pancreas. It is safer than an ERCP as it is non-invasive and does not require ionising radiation.

Due to the non-invasive nature of MRCP, it does not permit interventions to be performed, such as stone extraction, stent insertion, or biopsy.

Abdominal Tests

Abdominal paracentesis involves the insertion of a needle into the peritoneal cavity to remove the fluid. This can be a diagnostic paracentesis (an ascitic tap) or therapeutic paracentesis (an ascitic drain).

An ascitic tap may be used to:

An ascitic drain may be used to relieve abdominal pain or respiratory distress secondary to ascites. See Ascites for more detail regarding interpreting ascitic taps.

Author