Diamine oxidase (DAO) activity (test for histamine intolerance)

The test measures the activity of the DAO (diamine oxidase) enzyme in the blood serum, which is responsible for the degradation of histamine – a substance naturally present in many foods.

The result is given as a percentage and shows the rate of histamine degradation, i.e., the functional activity of the enzyme.

Too low DAO activity leads to excessive accumulation of histamine and symptoms resembling allergic reactions.

The test may be helpful for people who experience symptoms after consuming certain foods rich in histamine, such as aged cheeses (e.g., Parmesan, cheddar), pickled foods, smoked and canned fish, tomatoes, chocolate, cocoa, and red wine. Assessment of DAO activity (the rate of histamine degradation) provides additional information that can support the diagnostic process conducted by a physician.

Factors influencing the diamine oxidase (DAO) activity:

• physiological condition - during pregnancy, histamine tolerance increases due to the production of DAO by the placenta;
• genetic predisposition;
• medications and food that reduce the DAO activity;
• damage to the intestinal mucosa.

Symptoms that may indicate the DAO deficiency

An increase in serum histamine levels is responsible for the occurrence of undesirable conditions. The most common symptoms include:

• gastrointestinal complaints (e.g. nausea, vomiting, abdominal pain);
• rash, hives, eczema;
• migraine;
• dizziness;
• drop in arterial blood pressure;
• chronic fatigue.

The test involves taking a blood sample from the patient. It does not require any special preparation by the patient. It is recommended that it be performed in the morning, after a full night's rest. Immediately before the sample is taken, the patient should rest for about 15 minutes and drink a glass of water about 30 minutes beforehand.

Before the test, it is advisable to consult your doctor about the possibility of temporarily discontinuing any medications that may affect DAO enzyme activity. Any changes in pharmacotherapy should always be made by a doctor. 

When and how to collect the results?

The test results are usually available 14 working days after the sample is taken. For detailed information, please contact the facility where the test will be performed or ask directly at the reception desk. 

DAO test — reference values

Normal DAO enzyme activity indicates normal histamine metabolism. A low result may indicate histamine intolerance caused by enzyme deficiency or impaired enzyme activity.

Approximate reference values may vary depending on the laboratory. The result is given as a percentage and shows the rate of histamine degradation, i.e., the functional activity of the enzyme.