How to Diagnose CSID

Getting a correct diagnosis for Congenital Sucrase-Isomaltase Deficiency (CSID), can be a grueling journey. Starting with a pediatrician or primary care physician, an individual may be diagnosed with more common causes of diarrhea such as toddler’s diarrhea, irritable bowel syndrome, parasites, or intestinal infections. When treatments for these conditions do not relieve symptoms, the individual may be referred to a gastroenterologist, who specializes in digestive ailments.

Like the primary care physician and pediatrician, a gastroenterologist conducts a physical examination and discusses one’s clinical, family, and dietary history. Based on this information, tests may be ordered. As is often seen with rare diseases, the journey to determine the correct diagnosis may require a systematic process of elimination of other more common ailments before an exact diagnosis can be confirmed.

Testing for CSID

Different tests are available to help in the diagnosis of CSID. Contributing factors, like the age and health of the individual, may affect the tests a physician chooses to order. Your doctor may even recommend a short treatment period with a drug known to treat this disorder. If you show improvement, you may have CSID. The most accurate test available for this condition is an upper gastrointestinal endoscopic procedure using a scope to obtain tissue biopsies (small samples of tissue) from the small intestine. The biopsied tissue is analyzed by a special lab for the level of sucrase and isomaltase enzyme activity present. It is considered the definitive test for diagnosing CSID. However, due to the invasive nature of this test, your doctor may decide to wait to perform this test and suggest other noninvasive tests instead. Two of the tests your doctor may order, which are based on the gas content in your exhaled breath, provide useful information to help in the diagnosis. A sugar challenge test could also be used.

Gastrointestinal Endoscopy Test

During the gastrointestinal endoscopy test, several biopsies (tissue specimens) are obtained from the small intestine and sent for a specialized analysis of enzymatic activity of a number of disaccharide enzymes, including sucrase and isomaltase. The laboratory analysis that determines this enzyme activity is commonly known as a disaccharidase assay via a small bowel biopsy. After measuring the activity of these intestinal disaccharidases (lactase, sucrase, isomaltase or palatinase, and maltase-glucoamylase), a definitive diagnosis of the presence or absence of CSID can be made.

Breath Tests

Sucrose Hydrogen Methane Breath Test

The sucrose hydrogen methane breath test is a noninvasive test in which levels of hydrogen gas in an individual’s breath are measured following sucrose ingestion. This test is based on the fact that bacteria in the large intestine are capable of producing hydrogen gas in the human gut. These bacteria produce hydrogen gas when they are exposed to unabsorbed food, particularly sugars and carbohydrates. Large amounts of hydrogen gas are produced when there is a problem with the digestion or absorption of food in the small intestine, allowing more unabsorbed food to reach the large intestine. Thus, an increase in hydrogen gas in exhaled breaths after consuming a set amount of sucrose suggests that small intestinal enzymes are not working properly. While taking the test, individuals who have Sucrose Intolerance may experience unpleasant gastrointestinal symptoms due to the large amount of sucrose consumed during the test.

13C- Sucrose Breath Test

The 13C-Sucrose Breath Test is a simple, noninvasive breath test to quantify sucrase activity. The test uses a sucrose solution containing naturally occurring 13C as the test nutrient. Sucrose is broken down by sucrase which splits 13C-sucrose into 13C-glucose and 13C-fructose. These sugars are absorbed through the mucosal cells and will be metabolized in the liver, releasing 13CO2, which is transported by the blood to the lungs where it is expelled in the breath. The release of 13CO2 in breath correlates with the amount of sucrase activity in the small intestine. In addition to releasing lower levels of 13CO2, people with sucrase deficiency may experience gastrointestinal symptoms following the consumption of the sucrose required as the test nutrient.

Sugar Challenge Test

The 4-4-4 Sugar Challenge Test is a simple, short test that can be performed by the individual at home. Stir 4 tablespoons of table sugar into 4 ounces of water and drink it on an empty stomach. If symptoms (bloating, gas, and/or diarrhea) occur during the next 4 to 8 hours, this is suggestive of decreased sucrase activity. This test is not appropriate for infants, young children, geriatric patients, and those with co-morbid conditions like diabetes. Patients may have severe symptoms if they are very sensitive to sugar. A physician should be consulted before this test is taken.

Sucrose Intolerance May Be More Common Than You Think