How Is CSID Diagnosed?

Most CSID patients begin their diagnosis journey at their pediatrician or primary care physician (PCP). PCPs may diagnose patients with more common causes of diarrhea such as toddler’s diarrhea, irritable bowel syndrome, parasites, or intestinal infections. When treatment for these more common conditions does not alleviate symptoms, a primary care physician will refer the patient to a gastroenterologist, a doctor who specializes in digestive dysfunction.


After referral to a gastroenterologist, the physician will perform a routine analysis of patient well-being, physical examination, clinical history, family history, and diet 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 sometimes 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) will be obtained from the duodenum, the first part of the small intestine, and sent for a specialized laboratory analysis of enzymatic activity. This laboratory analysis is commonly known as a disaccharidase assay test using a small bowel biopsy. Measuring intestinal disaccharidases (lactase, sucrase, isomaltase or palatinase, and maltase) through small bowel biopsy is considered the gold standard for diagnosing CSID or Genetic Sucrase-Isomaltase Deficiency (GSID).


Depending on the age of the patient, 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 in the breath to diagnose gastrointestinal disorders. In the human gut, only a specific type of bacteria in the large intestine is capable of producing hydrogen. The bacteria produce hydrogen when they are exposed to unabsorbed food, particularly sugars and carbohydrates. Large amounts of hydrogen 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 breath hydrogen output suggests that small intestinal enzymes are not working properly. The hydrogen breath test is not always accurate in identifying CSID since other gastrointestinal conditions can also produce a positive hydrogen breath test. It is also likely to produce gastrointestinal symptoms as a significant amount of sugar is consumed in preparation for this test.


As of 2017, a 13C-sucrose breath test has been proposed to accurately diagnose CSID, but it is not easily obtained. Although this test is considered investigational, it holds great promise for someday being a diagnostic tool.


A stool pH test can sometimes be conducted, but the results are not specific for sucrose malabsorption. If a physician orders a stool pH test in the process of diagnosing CSID, he/she would be looking for a lower-than-normal pH level.


When there is difficulty in diagnosing Genetic Sucrase-Isomaltase Deficiency or the diagnosis is in doubt, a short therapeutic trial with Sucraid® (sacrosidase) Oral Solution may be warranted to assess the response in a patient who is suspected of having sucrase deficiency. Sucraid® has been approved as a diagnostic tool for sucrase deficiency as written in the Sucraid® package insert.



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


Test MethodInfo Regarding Test Method
Small Bowel Biopsy with Disaccharidase Enzyme Testing• Gold standard for diagnosing sucrase deficiency

• Requires an invasive procedure called an upper endoscopy or EGD

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

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

• Must catch breath into 6 tubes over a 3-hour time period after ingesting a sucrose solution

• Patients with sucrase deficiency may experience symptoms due to the large consumption of sucrose
4-4-4 Oral Sugar Challenge• The test is short, simple and can be performed in the privacy of the patient’s home

• 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 4-8 hours; this suggests sucrose intolerance is possible