The sucrose breath test is a non-invasive diagnostic tool used to investigate digestive symptoms related to table sugar consumption. This test measures specific gases in a person’s exhaled breath after they drink a sucrose solution. It determines if the body is effectively breaking down and absorbing sucrose in the small intestine. An abnormal result provides clarity for individuals experiencing chronic, unexplained gastrointestinal distress such as bloating or diarrhea.
The Scientific Basis of the Test
Sucrose is a disaccharide that must be broken down into simpler sugars before the body can absorb it. This digestive process relies on the sucrase enzyme, located on the brush border of the small intestine’s lining. The enzyme splits the sucrose molecule into glucose and fructose, which are then readily absorbed into the bloodstream.
When the sucrase enzyme is deficient, the sucrose passes undigested into the large intestine, or colon. Bacteria there ferment the unabsorbed sucrose, releasing gases as a byproduct.
The two main gases produced are hydrogen (\(\text{H}_2\)) and methane (\(\text{CH}_4\)). These gases are absorbed into the bloodstream, travel to the lungs, and are ultimately expelled through the breath. The test measures the concentration of these specific gases in the exhaled air over time to indirectly assess the efficiency of sucrose digestion.
Conditions Identified by the Sucrose Breath Test
The test diagnoses Sucrase-Isomaltase Deficiency (SID), a condition where the body produces insufficient enzymes required to break down sucrose and certain starches. This deficiency can be congenital (genetic) or acquired later in life due to damage to the small intestine lining caused by gastrointestinal diseases or infections.
Symptoms prompting a sucrose breath test include chronic, watery diarrhea, abdominal bloating, excessive flatulence, and cramping, particularly after consuming high amounts of sugar. These symptoms occur because the undigested sugar draws excess water into the intestine, leading to osmotic diarrhea. In children, this condition can manifest as a failure to thrive or poor weight gain.
A sustained rise in hydrogen or methane levels following the sucrose drink indicates that sugar reached the colon undigested. The sucrose breath test is an important step in differentiating these symptoms from other common digestive disorders like Irritable Bowel Syndrome (IBS) or other forms of carbohydrate malabsorption.
Patient Preparation and Procedure
Accurate results depend on careful patient preparation to ensure the digestive tract is clear of interfering substances. Patients must avoid antibiotics for four weeks prior to the test, and stop taking laxatives and promotility drugs for one week beforehand. A restricted diet must be followed for 24 hours, focusing on low-fiber, easily digestible foods like white rice, plain baked meat, and eggs.
The patient must also fast completely for 12 hours before the test begins, allowing only water intake, to establish a baseline reading. On the day of the test, a baseline breath sample is collected by having the patient blow into a specialized tube or bag. This confirms the starting levels of hydrogen and methane gas before any sucrose is consumed.
Following the baseline collection, the patient drinks a solution containing a measured dose of sucrose dissolved in water. Subsequent breath samples are collected at timed intervals, typically every 30 minutes for two to three hours. A laboratory analyzes these sequential samples for a noticeable spike in \(\text{H}_2\) or \(\text{CH}_4\) levels, which confirms a diagnosis of sucrose malabsorption.