Breath Test Endpoints,
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Isotopes Science

Methionine Breath Test

A rapid, non-invasive test that quantifies liver mitochondrial function. ¹³C-methionine is metabolized exclusively in hepatic mitochondria, and ¹³CO₂ in breath correlates wdith disease severity. 

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 here.

Octanoate Breath Test

A sensitive biomarker for mitochondrial β-oxidation, with strong correlation to insulin resistance and predictive value for NASH.

Mitochondrial β-oxidation impairment is a hallmark of several liver diseases, including nonalcoholic steatohepatitis (NASH). The Octanoate Breath Test uses sodium 1-¹³C-octanoate, which undergoes β-oxidation in the liver. When mitochondrial function is compromised, reduced oxidation alters the appearance of ¹³CO₂ in breath.

Clinical studies show this test correlates with insulin resistance and is predictive of NASH, making it a powerful non-invasive biomarker for early detection and disease monitoring.

Methacetin Breath Test

A rapid test of hepatic cytochrome P450 activity. ¹³C-methacetin metabolism produces ¹³CO₂, allowing accurate assessment of liver damage within 60 minutes.

Methacetin is metabolized rapidly by hepatic microsomal enzymes. After oral administration of ¹³C-methacetin, cytochrome P450 1A2 converts it via O-dealkylation to acetaminophen and ¹³CO₂
. 
The ¹³C-methacetin breath test (MBT) has demonstrated 95% sensitivity and 97% specificity in distinguishing between early cirrhotic and non-cirrhotic patients. The test can be completed within 60 minutes and is available in custom kit format for clinical research studies.

Custom kits are available for clinical research studies. See more information about the Methacetin Breath Test.

Caffeine Breath Test

A specific assay for cytochrome P450 1A2 activity, using ¹³C-caffeine metabolism to quantify enzyme function.

The ¹³C-caffeine breath test is highly specific for P450 1A2 isoenzyme activity, which catalyzes caffeine 3-N-demethylation.

Following oral administration, breath samples are collected for one hour. Enzyme activity is quantified by analyzing the ¹³CO₂:¹²CO₂ ratio via isotope ratio mass spectrometry. This provides a reliable, non-invasive measurement of cytochrome P450 1A2 function in vivo.

See more information about the Caffeine Breath Test here.

Phenylalanine Breath Test

Assesses hepatic cytosolic capacity by tracking phenylalanine metabolism. ¹³C-phenylalanine conversion to ¹³CO₂ provides a quantitative, non-invasive measure of liver function in end-stage disease.

Liver disease is associated with abnormal elevations in plasma concentrations of aromatic amino acids, including phenylalanine and tyrosine. The liver is the primary site of their metabolism, particularly hydroxylation of phenylalanine to tyrosine and subsequent degradation.

The Phenylalanine Breath Test uses L-[1-¹³C]phenylalanine, a safe, non-radioactive tracer. The appearance of ¹³CO₂ in breath provides a quantitative measure of hepatic cytosolic metabolic capacity. Multiple studies demonstrate its ability to assess cytosolic function in patients with end-stage liver disease.

See more information about the Phenylalanine Breath Test here.

Urea Breath Test

A non-invasive test to detect Helicobacter pylori infection by measuring ¹³CO₂ in breath after ingestion of ¹³C-urea.

The urea breath test (UBT) detects urease activity of Helicobacter pylori (H. pylori) in the stomach. After administration of ¹³C-urea, bacterial urease converts it to ammonia and ¹³CO₂, which is measured in expired breath.

Defined cutoff levels indicate infection and can also confirm eradication after antibiotic treatment. UBT is widely used due to its high sensitivity, specificity, and patient-friendly procedure.

Small Intestinal Bacterial Overgrowth (SIBO) Breath Test

Identifies bacterial overgrowth in the small intestine by tracking hydrogen and methane production after lactulose or glucose ingestion.

Small intestinal bacterial overgrowth (SIBO) occurs when normally sterile small intestines are colonized with bacteria, reducing nutrient absorption and causing inflammation. The SIBO breath test uses lactulose or glucose as a substrate; bacterial fermentation produces hydrogen and methane, which are detected in exhaled breath. Elevated gas levels over time confirm bacterial overgrowth, supporting diagnosis and treatment planning for functional GI disorders.

Lactose Breath Test

Detects lactose intolerance by measuring hydrogen and methane in breath after lactose ingestion. 

Lactose intolerance results from the body’s inability to break down the milk sugar lactose, leading to colonic gas, diarrhea, and abdominal pain. After administration of lactose, bacterial fermentation produces hydrogen and methane gases, which are measured in exhaled breath.

This hydrogen breath test provides a reliable, non-invasive way to confirm lactose intolerance and support dietary management.

Fructose Breath Test

Assesses fructose malabsorption by tracking hydrogen levels after a standardized oral fructose load.

Fructose malabsorption occurs when the small intestine cannot absorb fructose efficiently. Unabsorbed fructose passes into the colon, where it is fermented by bacteria, producing hydrogen and causing bloating, abdominal pain, and diarrhea.

The hydrogen breath test, following a 25 g oral dose of fructose, provides a quantitative readout of malabsorption, aiding diagnosis and treatment planning.

Sucrose Breath Test

Evaluates small intestine brush border enzyme activity, detecting damage from infection, trauma, or disease.

The Sucrose Breath Test (SBT) assesses the health and functional capacity of the intestinal brush border. In conditions such as infection, surgical trauma, chronic disease, or chemotherapy, brush border activity may be impaired, reducing sucrose digestion. 

After ingestion of ¹³C-sucrose, reduced ¹³CO₂ in breath indicates decreased enzyme activity. The SBT is safe, validated, and provides a sensitive measure of small intestinal function in both research and clinical settings.

See more information about the Sucrose Breath Test here.

Breath Tests for Pancreatic Function

Quantify Pancreatic Lipase Activity with Reproducible Biomarkers

The most widely researched pancreatic function breath test. Assesses pancreatic lipase activity by measuring ¹³CO₂ in breath after ingestion of a labeled triglyceride meal.

The Mixed Triglyceride Breath Test (MTBT) is designed to evaluate pancreatic exocrine function, specifically lipase activity in the duodenum. 


The test uses a triglyceride labeled with ¹³C-octanoate at the central glycerol position and long-chain stearate fatty acids at positions 1 and 3. After ingestion with a meal, the triglyceride is hydrolyzed by pancreatic lipases into fatty acids. These fatty acids are absorbed and transported to the liver, where oxidation produces ¹³CO₂ measurable in expired breath. 


The rate of ¹³CO₂ appearance directly reflects pancreatic lipase activity, providing a validated, non-invasive tool for assessing pancreatic function in both clinical and research settings.

Breath Tests for Oro-Cecal Transit Time

Generate Regulator-Trusted Gut Motility Endpoints Without Invasive Methods

Measures oro-cecal transit time using ¹³C-labeled glycosyl ureides. The rise of ¹³CO₂ in breath reflects when the substrate reaches the colon.

The ¹³C Lactose Ureide Breath Test provides a validated, non-invasive method to assess oro-cecal transit time — the time required for material to move from the mouth to the cecum. 


Intestinal brush border enzymes cannot split the glycosyl ureide bond between sugar and urea, but colonic bacteria can. Once the substrate reaches the colon, bacterial metabolism releases ¹³CO₂, which appears in expired breath. The initial rise in ¹³CO₂ precisely determines oro-cecal transit time, offering a reproducible measure of gut motility that is valuable in both clinical diagnostics and research studies. providing a validated, non-invasive tool for assessing pancreatic function in both clinical and research settings.