Historically, the definitive test for diagnosing sucrase deficiency and Congenital Sucrase-Isomaltase Deficiency (CSID) has been a test called the disaccharidase assay. This assay requires a diagnostic procedure usually performed by a gastroenterologist (physician who specializes in the gastrointestinal system). This procedure (called endoscopy) involves the insertion into the body of a scope, which is an instrument used to view internal areas of the body. Gastroenterologists use endoscopic procedures to examine various areas of the intestinal tract. If warranted, a gastroenterologist will obtain a tiny tissue sample from the wall of the intestinal tract, for evaluation with a disaccharidase assay in a special laboratory.
When a patient, based on their symptoms and family history, is suspected of having CSID, a gastroenterologist might perform an endoscopic procedure to view the small intestine and obtain tiny tissue samples from this area. Obtaining tissue samples only takes about 15 minutes, but a mild anesthesia is required. The tissue samples are then sent to a special laboratory that measures the extent of the activity of the enzymes present that are able to digest complex sugars. For patients suspected of having CSID, the enzyme of interest is sucrase-isomaltase, the enzyme that doesn’t work well in people with CSID.
The diagnosis of CSID may also be aided by either of two breath tests. Both tests can help detect whether the enzyme sucrase-isomaltase is working by examining one’s exhaled breath. The first is called the carbon-13 sucrose breath test, because one consumes a sugary drink of sucrose that contains a natural, stable version of carbon, called carbon-13(13C). If the patient has little or no working sucrase-isomaltase enzymes in their intestine, there will be less carbon-13 gas exhaled than if working sucrase-isomaltase enzymes were present. The carbon-13 breath test is thought to directly measure sucrase activity and, as such, is the most definitive test that can aid in the diagnosis of sucrase deficiency that does not require a procedure to obtain tissue samples from your intestine.
The second breath test is called the sucrose hydrogen breath test, which measures the amount of hydrogen gas one exhales after consuming a simple sugary drink. In this test, there will be higher than normal levels of hydrogen gas in your exhaled breath if there are little or no working sucrase-isomaltase enzymes in your intestine. There may be other reasons why one has higher than normal levels of hydrogen gas in one’s exhaled breath, so this second breath test may not be as accurate in detecting sucrase deficiency. Additionally, many people are not hydrogen producers naturally, so the test may create a false negative in those individuals.