Diamine oxidase (DAO) is an enzyme that manages histamine in the body. The DAO blood test is a specialized tool used by practitioners to investigate potential histamine intolerance. Histamine is a naturally occurring biogenic amine involved in processes like allergic reactions, stomach acid secretion, and nerve signaling.
Histamine is present both in the body, produced by immune cells, and in many foods. If the body struggles to break down dietary histamine, it can build up, leading to non-allergic symptoms known as histamine intolerance. The DAO test measures the body’s capacity to process this compound, offering insights into why certain foods may trigger adverse reactions.
The Biological Function of Diamine Oxidase
Diamine Oxidase is a copper-dependent enzyme that acts as the primary mechanism for breaking down histamine ingested through food (exogenous histamine). This digestive enzyme is predominantly produced in the lining of the small intestine by enterocytes. Its function is to prevent excessive histamine from entering the bloodstream and causing systemic reactions.
The enzyme works by initiating an oxidative deamination process, inactivating the histamine molecule by converting it into imidazole acetaldehyde, which the body can then excrete. DAO acts as a biochemical barrier within the gut, ensuring that dietary histamine is degraded before absorption. When DAO activity is low, this protective barrier weakens, allowing histamine to pass through the intestinal wall and accumulate in the circulation. This accumulation leads to the symptoms of histamine intolerance.
Preparing for and Taking the DAO Test
The DAO test is a straightforward procedure that measures the activity level of the enzyme circulating in the blood. It requires a simple blood draw, similar to a standard cholesterol or metabolic panel. Obtaining an accurate result requires ensuring the patient is in a baseline state before sample collection.
Preparation typically involves fasting for eight to twelve hours to eliminate recent dietary histamine intake that could temporarily influence enzyme release. A significant preparation step involves reviewing all medications with a healthcare provider. Many common prescription and over-the-counter drugs, such as certain antidepressants, anti-inflammatories, and expectorants, inhibit DAO enzyme activity. These inhibitors can artificially lower the test result, potentially leading to a misdiagnosis, so temporary discontinuation may be necessary under medical guidance.
Deciphering DAO Test Results
The results of a DAO blood test are expressed as a measurement of enzyme activity, often in units per milliliter (U/mL). Normal DAO activity is typically considered above 10 U/mL, indicating the body has a capacity to degrade dietary histamine. A result in this range suggests that symptoms are unlikely to be primarily caused by a DAO deficiency.
When DAO activity falls below this threshold, it suggests a compromised ability to metabolize histamine. A moderate deficiency might range between 3 and 10 U/mL, while levels below 3 U/mL are classified as a severe deficiency. These low levels strongly correlate with a high probability of histamine intolerance, indicating a reduced capacity to handle the normal histamine load from a typical diet, leading to symptom-causing accumulation.
The clinical presentation of histamine intolerance can be wide-ranging, including digestive upset (bloating and diarrhea), headaches or migraines, skin flushing or rashes, and heart palpitations. While low DAO activity is a strong indicator, it does not confirm the diagnosis in isolation. Other factors, such as underlying inflammatory bowel conditions or genetic variations in the DAO-producing gene, can also contribute to low enzyme activity.
Lifestyle Adjustments Following Diagnosis
A confirmed low DAO activity level provides a clear path for management focused on reducing the histamine burden. The most immediate intervention is adopting a low-histamine diet. This modification centers on avoiding foods naturally high in histamine or those that trigger its release, particularly aged, fermented, or cured products like mature cheeses, cured meats, alcohol, and leftovers.
The dietary focus shifts toward fresh, unprocessed foods, which naturally contain lower histamine levels. Dietary adjustments can be supported by the targeted use of DAO supplements. These supplements are taken immediately before meals to introduce functional DAO into the digestive tract, assisting in the breakdown of dietary histamine before absorption.
Addressing the underlying cause of low DAO is a significant component of management. Since the enzyme is copper-dependent, ensuring adequate intake of necessary cofactors like copper, Vitamin C, and Vitamin B6 can support optimal DAO function. If the low enzyme activity is secondary to gut inflammation or another digestive disorder, treating that primary condition becomes the central strategy for restoring the body’s natural DAO production over time.