The Diamine Oxidase (DAO) test measures the activity of a specific enzyme in the bloodstream. This test provides insight into the body’s capacity to metabolize biogenic amines ingested through food. By quantifying the functional level of this enzyme, healthcare professionals can assess a person’s ability to process these amines. The results help guide evaluation for individuals experiencing unexplained symptoms related to dietary intake. The DAO test is a straightforward blood draw that offers objective data regarding gut health.
The Role of Diamine Oxidase
Diamine Oxidase is a digestive enzyme central to the metabolism of biogenic amines. It is primarily produced in the mucosal lining of the small intestine, and also in the kidneys and the placenta during pregnancy. Its main function is to break down excess biogenic amines, such as histamine, absorbed from food into the bloodstream. This process maintains balance within the digestive system and prevents systemic accumulation.
When functioning effectively, DAO acts as a barrier, ensuring that dietary histamine is rapidly degraded before entering circulation. The enzyme converts active histamine into an inactive metabolite through an oxidative deamination reaction. This metabolic process keeps circulating histamine levels in a healthy range following a meal.
DAO activity reflects the small intestine’s ability to protect the body from an overload of dietary amines. The DAO enzyme specifically targets histamine consumed from the diet.
Identifying Histamine Intolerance
The DAO test is used when a physician suspects histamine intolerance (HI). This is not a true allergy but a condition resulting from an imbalance between consumed histamine and the body’s ability to break it down. Reduced DAO activity allows ingested histamine to accumulate, leading to adverse effects that mimic an allergic reaction.
Symptoms of histamine intolerance are diverse and affect multiple organ systems, making diagnosis challenging. Patients often report migraines or vascular headaches, along with gastrointestinal disturbances like bloating, diarrhea, and abdominal pain. Other manifestations include skin issues such as flushing, hives, and itching, or respiratory symptoms like a congested or runny nose.
A DAO deficiency can arise from several factors. These include genetic variations affecting enzyme production or function. Gastrointestinal disorders, such as inflammatory bowel disease, can damage the intestinal lining where DAO is produced, leading to lower enzyme levels. Specific medications, including some antidepressants, anti-inflammatories, and acid-blocking drugs, are known to inhibit DAO activity.
Preparation and Procedure for the Test
The Diamine Oxidase activity test is a simple procedure requiring only a blood sample. It measures the functional activity of the DAO enzyme circulating in the blood, which is a reliable marker of the body’s histamine-degrading capacity. Blood is drawn from a vein in the arm, similar to any standard lab test.
Proper preparation ensures accurate results. Most laboratories require fasting for at least eight to ten hours before the blood draw. Patients are advised to maintain their usual diet unless instructed otherwise, helping capture a representative baseline of DAO function.
Patients must discuss all current medications with a healthcare provider, as some drugs can interfere with DAO activity and skew results. The physician may recommend temporarily discontinuing known DAO-inhibiting medications before the test. The sample is then sent to a laboratory where the enzyme’s activity is measured.
Decoding Your DAO Test Results
The results of a DAO activity test are reported in Histamine Degrading Units per milliliter (HDU/mL) and interpreted based on reference ranges. A result greater than 80 HDU/mL reflects normal DAO activity, suggesting adequate capacity to metabolize dietary histamine. This indicates that symptoms are likely not due to a primary DAO deficiency.
Results falling between 40 and 80 HDU/mL are classified as reduced activity. This intermediate level suggests moderate impairment in histamine breakdown, which may cause symptoms when consuming high-histamine foods. A result below 40 HDU/mL strongly indicates a significant DAO deficiency and supports a diagnosis of histamine intolerance alongside compatible symptoms.
A low result prompts management strategies focused on reducing the body’s histamine load. The primary intervention is a trial of a low-histamine diet, which restricts aged, fermented, and cured foods high in the compound. This dietary modification improves symptoms for many patients.
Management also involves DAO enzyme supplements, taken before meals to assist the breakdown of dietary histamine in the gut. These supplements provide an external enzyme source to compensate for the deficiency. A comprehensive plan also addresses underlying causes of low DAO activity, such as gut health issues or medication use.