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Important Diagnostic Information

Most patients with Genetic Sucrase-Isomaltase Deficiency/Congenital Sucrase-Isomaltase Deficiency begin their diagnosis journey at their pediatrician or primary care physician’s office. Primary care physicians may diagnose patients with more common causes of diarrhea, such as toddler’s diarrhea, Irritable Bowel Syndrome, parasites or intestinal infections. When treatments such as antibiotics for these more common conditions do not alleviate symptoms, the physician will refer the patient to a gastroenterologist, a physician who specializes in digestive dysfunction.

The gastroenterologist will perform a routine analysis of patient well-being, including a physical examination, clinical history, family history and diet history, and may order tests to determine the exact diagnosis. With rare diseases, such a discovery process is often needed to systematically eliminate the possibility of more common ailments. If Genetic Sucrase-Isomaltase Deficiency is suspected, the diagnostic workup should include an upper gastrointestinal endoscopy, in which several biopsies (tissue specimens) are obtained from the small intestine and sent for a specialized laboratory analysis of enzymatic activity. A laboratory analysis to determine sucrase-isomaltase activity is commonly known as a disaccharidase assay via a small bowel biopsy. The measurement of intestinal disaccharidases (lactase, sucrase, isomaltase or palatinase, and maltase) through a small bowel biopsy is considered the gold standard for diagnosing Genetic Sucrase-Isomaltase Deficiency.

Depending on the age of the patient, the treating physician may decide that the endoscopic procedure is not appropriate. Instead, they may try the patient on a brief trial with Sucraid® (sacrosidase) Oral Solution. If the physician decides against either of these approaches, he may try different tests which are not diagnostic for GSID/CSID but may help in making the correct diagnosis. Some of these tests are listed in the table below. For example, the physician may order a sucrose hydrogen breath test, which measures the level of hydrogen in the breath to help aid in the diagnosis of 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, then, suggests that small intestinal enzymes are not working properly although the physician will still have to determine if this is due to GSID/CSID. The sucrose hydrogen breath test is noninvasive, short in duration and can be administered by the patient at home. Patients with sucrase deficiency may experience symptoms due to the large consumption of sucrose. A free Sucrose Intolerance Hydrogen Breath Test is available through your healthcare provider. For more information or to order a test kit, call 1-800-705-1962.

The treating physician also may recommend a stool pH test, since Genetic Sucrase-Isomaltase Deficiency often causes low pH or highly acidic stools. The results of the stool pH test, however, are not specific for sucrose malabsorption.

It may sometimes be clinically inappropriate, difficult or inconvenient to perform a small bowel biopsy or breath test to make a diagnosis of Genetic Sucrase-Isomaltase Deficiency. If the diagnosis is unclear, a short therapeutic trial (e.g., two weeks) with Sucraid® (sacrosidase) Oral Solution may be warranted to assess the response in a patient who is suspected of having sucrase deficiency. Sacrosidase is a yeast-based enzyme that replaces sucrase. Sucraid® is indicated for a therapeutic trial for genetically determined sucrase deficiency.1

Tests for Genetic Sucrase-Isomaltase Deficiency/Congenital Sucrase-Isomaltase Deficiency

Diagnostic Tests
Test Method
Info Regarding Test Method
Small Bowel Biopsy with Disaccharidase Enzyme Testing
  • Definitive for diagnosing sucrase deficiency
  • Requires an invasive procedure called an upper endoscopy or EGD
  • Sample requires rapid freezing and transfer to a specialized laboratory
Sucraid® Therapeutic Trial
  • Sucrase enzyme replacement therapy
  • A 2-week sample of a medication called Sucraid®, which is an exogenous enzyme
Tests That Aid in Diagnosis
Test Method
Info Regarding Test Method
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
13C Sucrose Breath Test
  • Noninvasive
  • Newer procedure
  • Requires fasting for at least 3 hours
  • Must fill breath bags over a 3-hour time period after ingestion of sucrose and glucose
  • Mass spectrometry
  • Specific test for Genetic Sucrase-Isomaltase Deficiency
  • Does not produce symptoms in Genetic Sucrase-Isomaltase Deficiency patients because it does not require excessive consumption of sucrose
Stool pH Test
  • An indirect test for carbohydrate malabsorption
  • Not specific for sucrose malabsorption
Oral Sucrose Tolerance Test
  • Noninvasive procedure
  • Not specifically designed for diagnosing Genetic Sucrase-Isomaltase Deficiency
SI Genetic Test
  • Noninvasive procedure
  • Analysis of sucrase-isomaltase exon for the presence of one of 37 known
    pathogenic polymorphisms
  • Genetic sample collected via buccal swab on the inside of cheek
  • A positive genetic test supports the diagnosis of GSID. If patients are symptomatic and a negative genetic test is received, consult a physician or QOL Medical.


  1. Sucraid® (sacrosidase) Oral Solution Full Prescribing Information.
QOL Medical, LLC

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