How Is CSID Diagnosed?

Most of you with Congenital Sucrase-Isomaltase Deficiency (CSID) began your diagnostic journey in the office of your pediatrician or primary care physician. Primary care physicians may reach a presumptive diagnosis of one of the more common causes of chronic diarrhea, such as toddler’s diarrhea, irritable bowel syndrome, parasites, or intestinal infections. When treatments for these more common conditions do not alleviate the gastrointestinal symptoms, a primary care physician or pediatrician may refer you to a gastroenterologist, a doctor who specializes in digestive dysfunction.

Following a referral, a gastroenterologist performs a routine analysis of your well-being, a physical examination, clinical history, family history, and dietary history. Based on this information, the physician may order tests to determine the exact diagnosis. Often with rare diseases, there is a process of discovery that requires a systematic process of elimination of other more common ailments.

If CSID is suspected, the diagnostic workup could include an upper gastrointestinal endoscopy in which several biopsies (tissue specimens) are obtained from the distal duodenum or jejunum of the small intestine, and sent to a specialized laboratory for analysis of enzymatic activity. This laboratory analysis is commonly known as a disaccharidase assay, which is a test performed on the tissue specimens removed during the small bowel biopsy. Measuring intestinal disaccharidases (lactase, sucrase, isomaltase or palatinase, and maltase) in the tissue specimens obtained during the small bowel biopsy is the historically definitive assay for diagnosing CSID.

Depending on your age, a treating physician may order a sucrose hydrogen breath test. The hydrogen breath test is a test that can aid in the diagnosis of sucrase deficiency. It uses the measurement of hydrogen gas in exhaled breath to diagnose gastrointestinal disorders.

In the human gut, only a specific type of bacteria in the large intestine is capable of producing hydrogen gas. The bacteria produce hydrogen gas when they are exposed to unabsorbed food, particularly sugars and carbohydrates. Large amounts of hydrogen gas may be 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.

An increase in hydrogen gas in exhaled breath suggests small intestinal enzymes are not working properly. The hydrogen breath test is not specific for identifying CSID, since other gastrointestinal conditions can also produce a positive hydrogen breath test. This test is also likely to produce gastrointestinal symptoms in those with CSID, since a significant amount of sugar is consumed in preparation for this test.

The 13C-Sucrose Breath Test is a simple, noninvasive test that measures how well you metabolize sucrose. In this assessment, you consume a few ounces of a solution containing sucrose that has been labeled by naturally occurring 13carbon, referred to as 13C-sucrose. The 13C-Sucrose Breath Test also can produce uncomfortable gastrointestinal symptoms in patients with CSID, because a large consumption of sucrose is required with this test.

Normally, sucrose is broken down by sucrase in the small intestine, into two smaller and absorbable forms of sugar, glucose and fructose. When the sucrose is 13C-sucrose, the two absorbable sugars are also labeled with 13carbon, referred to as 13C-glucose and 13C-fructose. Once absorbed, these two sugars are absorbed and metabolized in the body. A byproduct of their metabolism is 13CO2, which is transported by the blood to the lungs where it is expelled in the breath.

The release of 13CO2 in your breath correlates with the amount of sucrase in the small intestine that is able to digest the consumed sucrose solution. When you take the breath test, samples of your exhaled breath are collected in specially sealed test tubes over a period of 90 minutes. If there is sufficient sucrase present in the small intestine, the amount of 13CO2 in your exhaled breath matches the levels of 13CO2 obtained from individuals known to have adequately functioning sucrase.

In addition to releasing lower levels of 13CO2, individuals with sucrase deficiency may experience gastrointestinal symptoms associated with sucrase deficiency following consumption of the sucrose solution.

When there is difficulty in diagnosing CSID or the diagnosis is in doubt, a short therapeutic trial with Sucraid® (sacrosidase) Oral Solution may be warranted to assess the response in an individual who is suspected of having sucrase deficiency. Sucraid® has been approved as a diagnostic tool for sucrase deficiency, as indicated in the Sucraid® package insert.3


Testing Methods to Aid in the Diagnosis of Congenital Sucrase-Isomaltase Deficiency


Test MethodInfo Regarding Test Method
Small Bowel Biopsy with Disaccharidase Enzyme Testing• Historically definitive assay for diagnosing sucrase deficiency

• Requires an invasive procedure called an upper GI endoscopy or EGD

• Sample requires rapid freezing and transfer to a specialized laboratory
Sucrose Hydrogen Breath Test• Noninvasive procedure

• Requires a special diet 24 hours before test and 12 hours of fasting

• Must capture exhaled breath in 6 tubes over a 3-hour time period after ingesting a sucrose solution

• The sucrose hydrogen breath test is likely to produce GI symptoms in patients with CSID, because a large consumption of sucrose is required with this test
4-4-4 Oral Sugar Challenge• The test is short and simple, and can be performed in the privacy of the patient’s individual’s home

• Discuss your symptoms and the 4-4-4 sugar challenge with your doctor before you take the challenge. The challenge can cause severe gas, bloating, and diarrhea, and may not be appropriate for infants, very young children, diabetics, or individuals with severe gastrointestinal symptoms

• Step 1: Stir 4 tablespoons of ordinary table sugar into a 4-ounce glass of water. Mix until sugar is completely dissolved

• Step 2: Drink it on an empty stomach

• Step 3: See if symptoms such as bloating, gas, and diarrhea occur during the next 4 to 8 hours; this result suggests sucrose intolerance is possible


  1. Opekun AR, Balesh AM, Shelby HT. Use of the biphasic 13C-sucrose/glucose breath test to assess sucrose maldigestion in adults with functional bowel disorders. Biomed Res Int. 2016;2016:7952891. doi:10.1155/2016/7952891
  2. University of Washington, Molecular Development Laboratory. Molecular diagnosis of congenital sucrase-isomaltase deficiency (CSID). SI gene sequence analysis. Last updated August 21, 2019.
  3. Sucraid® [package insert]. Vero Beach, FL: QOL Medical LLC; 2022.
  4. Nichols B, Adams B, Roah C, Ma C, Baker S. Frequency of sucrase deficiency in mucosal biopsies. J Pediatr Gastroenterol Nutr. 2012;55(suppl 2):S28-30. doi: 10.1097/01.mpg.0000421405.42386.64