Gastroenterology (Tests and signs) Flashcards
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.
Oesophagogastroduodenoscopy (OGD)
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.
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
LFTs often include:
- Bilirubin
- Alkaline phosphatase (ALP)
- Alanine transaminase (ALT)
- Aspartate transaminase (AST)
- Gamma-glutamyltransferase (GGT)
Actual measures of liver function:
- Albumin
- International normalised ratio (INR)
Other tests that may be considered are:
- Viral serology
- Autoantibodies (e.g. antinuclear, antimitochondrial, and anti-smooth muscle antibodies)
- Alpha-fetoprotein (AFP) – for hepatocellular carcinoma
- Ferritin and transferrin saturation – for haemochromatosis
- Caeruloplasmin – for Wilson’s disease
- Alpha-1 antitrypsin (A1AT)
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.
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
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:
- Hereditary and acquired causes of haemolytic anaemia:
- Gilbert’s syndrome – impaired bilirubin conjugation
Increased ALT and AST
A rise in AST and ALT greater than ALP and GGT suggests a hepatitic picture. Causes may be:
Toxic:
- Alcohol
- Paracetamol
- Infectious:
- Hepatitis A, B, C, D, and E
- HIV infection
- Plasmodium falciparum malaria
- Entamoeba haemolytica
- Leptospirosis
Autoimmune:
- Autoimmune hepatitis
- Primary biliary cirrhosis
- Primary sclerosing cholangitis
Other:
- Non-alcoholic fatty liver disease
- Wilson’s disease
- Hereditary haemochromatosis
- Alpha-1 antitrypsin deficiency
- Hepatocellular carcinoma
- Liver metastases
- Lymphoma
gallbladder and bileduct tests
Endoscopic retrograde cholangiopancreatography (ERCP)
Magnetic resonance cholangiopancreatography (MRCP)
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.
production of bilirubin
- In the reticuloendothelial cells, haem (found in haemoglobin) is converted to biliverdin and then converted to bilirubin.
- In the liver, bilirubin is converted into conjugated (direct) bilirubin, making it soluble and easier to excrete.
- Some bilirubin can escape the process and remain as unconjugated (indirect) bilirubin, which is insoluble.
- Conjugated bilirubin is excreted into the duodenum in bile. Once it reaches the colon, bacteria deconjugate the bilirubin and convert it into urobilinogen.
- 80% of this urobilinogen is eventually converted into stercobilin, giving faeces their colour.
- The remaining 20% is reabsorbed into the blood, which is processed in the liver for bile production.
- Some of the remaining 20% reaches the kidneys where it is oxidised into urobilin and excreted in the urine.
typical findings for jaundice depending on location
