How Do I Read My CSID Disaccharidase Biopsy Results?

When you receive your disaccharidase (digestive enzyme) assay biopsy results, you are looking at a measurement of how well the enzymes in your small intestine break down complex sugars into absorbable nutrients. These reports often contain complex metrics, but doctors look closely at the pattern of these numbers.

A pattern of low sucrase and low isomaltase activity combined with normal lactase activity often supports or raises suspicion for Congenital Sucrase-Isomaltase Deficiency (CSID) ^[1]. However, this pattern does not automatically confirm a genetic diagnosis. Your doctor will interpret these numbers alongside your symptoms and the physical health of your tissue samples ^[2].

What This Test Can and Cannot Tell You

• It measures sampled activity: It shows enzyme activity in the specific tiny pieces of tissue removed during your endoscopy, not necessarily your entire intestine ^[3].
• It does not prove genetics: Low numbers show a deficiency, but they do not automatically prove the deficiency is primary (inherited genetically).
• Handling matters: Results can be heavily influenced by how quickly the tissue was frozen and handled at the lab ^[4].
• Symptoms vary: A low enzyme value alone does not guarantee that carbohydrate maldigestion is the only cause of your symptoms ^[5].

What Does “U/g Protein” Mean?

You will likely see your enzyme activity measured in U/g protein (Units per gram of protein) ^[6][7].

Because the tiny tissue samples taken during an endoscopy vary in size, the lab normalizes the enzyme activity against the amount of protein in the sample. This ensures the measurement reflects enzyme activity rather than just the size of the biopsy piece ^[7]. While this helps standardize the measurement, it does not eliminate the risk of errors from poor specimen handling or from the specific location where the biopsy was taken ^[4].

Check Your Lab’s Reference Range First

Different laboratories use different assay methods and populations to determine their cutoffs. Always compare your numbers to the reference limits printed on your specific lab report.

For context, large clinical studies have often used the following numbers as example lower limits of normal ^[6]:

• Sucrase: 25 U/g protein
• Maltase: 100 U/g protein
• Lactase: 10 to 15 U/g protein
• Palatinase: 5 to 9 U/g protein

Understanding the Terminology:

• Palatinase: Laboratories often use palatinase as a surrogate (substitute) measure to estimate your isomaltase activity, though it isn’t a direct, pure measurement of all isomaltase function ^[8].
• Maltase-glucoamylase: Another enzyme complex that helps digest starches. Because it overlaps with sucrase-isomaltase, maltase numbers can be tricky to interpret ^[8].

What Your Number Patterns Might Mean

The pattern of your results provides clues about what is happening in your gut.

• Low Sucrase with Normal Lactase: This pattern raises clinical suspicion for primary CSID ^[1]. It suggests the specific mechanism that creates sucrase is impaired, while the rest of the intestine is healthy enough to produce lactase. However, it requires clinical context to confirm.
• Variable Palatinase (Isomaltase): While sucrase is generally low in CSID, your isomaltase (palatinase) activity can range from completely absent to nearly normal ^[9].
• Maltase Complexity: Maltase activity is influenced by both the sucrase-isomaltase and maltase-glucoamylase enzymes ^[8]. Your doctor will evaluate maltase in the context of your overall enzyme pattern.
• Low Across the Board: If all your enzymes (including lactase) are low, it might point to secondary damage—meaning another condition temporarily damaged your intestine. Conditions like celiac disease or inflammation can cause villous blunting (flattening of the intestinal absorptive surface) and reduce all enzyme production ^[10]. Alternatively, an all-low result could simply mean the tissue sample was inadequate or degraded before reaching the lab ^[4].

Understanding Enzyme Ratios

Some laboratory reports include ratios, such as a sucrase-to-lactase ratio. While these ratios can help your doctor spot descriptive patterns, there is no universally validated ratio threshold for diagnosing CSID ^[11]. Therefore, absolute activity values and the physical health of the tissue sample carry more weight than ratios alone.

Next Steps and Additional Testing

Because a biopsy only provides a snapshot of your tissue, your doctor may recommend additional testing to build a complete diagnosis ^[12]:

• Genetic Testing: A blood or saliva test can look for genetic mutations that cause CSID. However, tests may not detect every clinically relevant variant, and having a variant doesn’t guarantee you will have severe symptoms ^[13].
• Sucrose Breath Testing: A non-invasive test measuring how well you digest sucrose. Keep in mind that breath tests can be affected by other factors like bacterial overgrowth (SIBO) or how fast food moves through your gut ^[4].

Do not make extreme, long-term changes to your diet—like cutting out all carbohydrates—based solely on a lab report without guidance from a doctor or registered dietitian.