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Liver Function Breath Tests

Breath Tests

Metabolic Solutions can measure the conversion of any 13C-substrate to 13CO2. We have extensive experience with many different breath test protocols. Please contact us for help with your breath test needs.

Breath Test for Assessing Small Intestinal Health

Metabolic Solutions has obtained the exclusive North American license to the 13C Sucrose Breath Test (SBT) for assessing the health and function of the small intestine. Serious health ramifications can result if the functional area of the brush border is significantly reduced by damage caused by infection, surgical trauma, disease, antibiotics, use of certain drugs, and chemotherapy treatments. Read More

Breath Tests for Measuring Liver Function

Standard serologic and biochemical serum liver tests have been used to determine the presence of liver disease. However, these tests do not provide an accurate assessment of hepatic functional capacity nor do they detect changes in hepatic disease severity. A range of breath tests is available from Metabolic Solutions to quantitate liver function. These breath tests use natural metabolic substances labeled with a non-radioactive isotope of carbon. Breath tests determine the rate of appearance of labeled carbon dioxide to estimate various metabolic pathways of interest.

Metabolic Solutions can provide assistance with the following liver function breath tests:

New Breath Test

Methacetin Breath Test: Methacetin is metabolized rapidly by hepatic microsomal enzymes. When 13C-methacetin is orally administered, it undergoes extensive liver first-pass clearance. Cytochrome P450 IA2 in liver cells converts methacetin via O-dealkylation to acetaminophen and 13CO2. The 13C-methacetin breath test (MBT) has been shown to accurately assess the degree of liver damage. The MBT can reliably distinguish between early cirrhotic and non-cirrhotic patients with 95% sensitivity and 97% specificity. The MBT can be completed within 60 minutes. Custom kits are available for clinical research studies. See more information about the Methacetin Breath Test.


Methionine Breath Test: Methionine is an essential amino acid that has important roles in various metabolic processes, including protein synthesis. The Methionine Breath Test uses 1-13C-methionine, which is a non-radioactive isotope and is metabolized exclusively by hepatic mitochondria. 13C-methionine metabolism within 20 minutes results in an increased concentration of 13CO2 in expired breath. The quantity of 13CO2 measured in breath correlates with liver disease severity. Our studies demonstrate the effectiveness of the Methionine Breath Test in measuring hepatic mitochondrial function in individuals with liver disease. See more information about the Methionine Breath Test.

Octanoate Breath Test: Impairment of mitochondrial beta-oxidation has been reported with several liver diseases such as nonalcoholic steatohepatitis (NASH). Sodium 1-13C-octanoate undergoes liver mitochondrial beta-oxidation. The sodium 1-13C-octanoate breath test was found to correlate with insulin resistance and predict the presence of NASH.


Phenylalanine Breath Test: Liver disease is associated with an abnormal elevation of the plasma concentrations of the aromatic amino acids, phenylalanine and tyrosine. The liver is the principal site of aromatic amino acid metabolism, particularly the hydroxylation of phenylalanine to tyrosine and further tyrosine degradation. We showed that the rate of hepatic phenylalanine metabolism can be quantitatively calculated from the appearance of 13CO2 in the breath using the non-radioactive tracer, L-[1-13C]phenylalanine. Many studies have demonstrated that the phenylalanine breath test quantitates hepatic cytosolic capacity in end-stage liver disease. See more information about the Phenylalanine Breath Test.

Cytochrome P450 Activity

Erythromycin Breath Test: The Erythromycin Breath Test is a quantitative in vivo measure of hepatic CYP3A4 activity (cytochrome P450), the most important drug-metabolizing enzyme present in the liver. The test provides a phenotypic measurement of individual variance in hepatic enzymatic activity due to factors such as disease, diet, concomitant medications as well as genetic differences. The Erythromycin Breath Test is simple and quick to perform, and can be easily added to existing research protocols. The test is performed by intravenously administering a trace amount of radioactive 14C labeled erythromycin and then measuring the amount of exhaled 14CO2. The test does not require special equipment; the patient simply blows up a single small balloon 20 minutes after the IV dose injection. The level of 14CO2 correlates with the level of hepatic CYP3A4 (cytochrome P450) enzyme activity. See more information about the Erythromycin Breath Test.

Caffeine Breath Test: The [13C]caffeine breath test is highly specific for P4501A2 isoenzyme activity, which catalyzes caffeine 3-N-demethylation. Breath samples are collected over 1 h after oral administration, and the enzyme activity is quantified via analysis of the ratio of 13CO2 to 12CO2 by isotope ratio mass spectroscopy. See more information about the Caffeine Breath Test.