Stable isotope breath testing provides a reliable measure of liver and pancreatic function. Use of 13C labelled
non-radioactive substrates provides safe and easy access to metabolic function tests without the need to refer to a nuclear medicine department. Breath tests are particularly helpful in assessing basal liver and pancreatic function and follow up status.
The MIGe Diagnostics Unit offers the following non-radioactive stable isotope breath tests:
• 13C-Mixed Triglyceride test of pancreatic function
• 13C-Methacetin Breath test of functional liver mass
Pancreatic function test using 13C-Mixed Triglyceride
Metabolic principle
1,3-distearyl-2-{carboxyl-13C}octanoylglycerol, otherwise known as 13C-Mixed Triglyceride passes through the stomach and is digested by lipase activity in the duodenum. The two distearyl groups have to be hydrolysed by pancreatic lipase before absorption and metabolism of the 13C-octanoyl monoglyceride. Thus, the oxidation to 13CO2 is dependent on the rate-limiting step of hydrolysis of the fatty acids.
Applications of 13C -Mixed Triglyceride Breath Test
The 13C-Mixed Triglyceride Breath Test assesses duodenal pancreatic lipase activity. It is therefore useful for the investigation of severe exocrine pancreatic insufficiency. If applied under strict conditions even mild to moderate forms can be assessed with high sensitivity and specificity.
Patient preparation
The patient should have fasted for 10 hours prior to the test. The patient must not drink carbonated water or soft drinks prior to the test since these might interfere with the results. Thirteen consecutive breath samples are exhaled at designated time points and the lipase activity can be extrapolated from the exhalation profile.
Liver function – 13C-Methacetin Breath Test
Metabolic principle
Methacetin is metabolised rapidly in normal subjects, due to high liver extraction. This implies that methacetin metabolism is mainly dependent on liver blood flow which is decreased in cirrhotic patients. Methacetin undergoes dealkylation by hepatic CYP1A2 to acetaminophen with the methoxy group being eliminated as 13CO2. The Methacetin Breath Test is a rapid and precise quantitative liver function test without any evidence of toxicities.
Applications of 13C -Methacetin Breath Test
The liver status of patients diagnosed with liver disease can be assessed or monitored non-invasively using the 13C-Methacetin Breath Test.
Patient preparation
The patient should be fasted for 8 hours prior to the test. Smoking should also be avoided for at least one hour prior to the test. Prior to the test, the patient should not drink carbonated water or soft drinks as these might interfere with the results.