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DAO Value Explained – Histamine Intolerance & Diagnosis

The DAO value measures the activity of the enzyme diamine oxidase in the blood and indicates potential histamine intolerance. A low value may suggest impaired histamine breakdown.

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Things worth knowing about "DAO Value"

The DAO value measures the activity of the enzyme diamine oxidase in the blood and indicates potential histamine intolerance. A low value may suggest impaired histamine breakdown.

What Is the DAO Value?

The DAO value refers to the measured activity of the enzyme diamine oxidase (DAO) in blood serum or plasma. Diamine oxidase is an enzyme produced primarily in the small intestine, where it is mainly responsible for breaking down histamine derived from food. Histamine is a biogenic amine found in many foods and plays important roles in the body, but in excess it can cause a wide range of symptoms.

A low DAO value indicates that the body is not producing enough diamine oxidase, or that the enzyme is not sufficiently active to effectively break down ingested histamine. This can lead to histamine intolerance, which manifests through a variety of complaints.

Reference Values and Interpretation

Reference ranges for the DAO value may vary slightly depending on the laboratory and the measurement method used. As a general guideline:

Normal DAO value: > 10 HDU/ml (Histamine Degradation Units per milliliter) – histamine breakdown is functioning adequately.
Borderline DAO value: 3–10 HDU/ml – reduced DAO activity is possible.
Low DAO value: < 3 HDU/ml – a strong indicator of histamine intolerance.

It is important to note that the DAO value alone is not sufficient for a definitive diagnosis of histamine intolerance. It should always be assessed in combination with clinical symptoms and additional diagnostic measures.

Causes of a Low DAO Value

A reduced DAO value can have various causes:

Genetic predisposition: Some individuals naturally produce less DAO due to genetic variants.
Intestinal disorders: Conditions such as Crohn's disease, ulcerative colitis, or damage to the intestinal mucosa can reduce DAO production.
Medications: Certain drugs, including antidepressants (e.g., MAO inhibitors), antihistamines, antibiotics, and pain relievers, can inhibit DAO activity.
Nutrient deficiencies: A lack of cofactors such as vitamin B6, copper, or vitamin C can impair DAO activity.
Alcohol: Alcohol inhibits the DAO enzyme and additionally promotes histamine release in the body.
Hormonal changes: Fluctuations in estrogen levels, such as during the menstrual cycle or pregnancy, can affect DAO activity.

Symptoms Associated With a Low DAO Value

A low DAO value and the resulting histamine intolerance can cause a wide range of complaints that often resemble other conditions:

Headaches and migraines
Skin reactions such as flushing, itching, or hives
Gastrointestinal symptoms (bloating, diarrhea, abdominal pain)
Runny or blocked nose (rhinitis)
Heart palpitations or a drop in blood pressure
Fatigue and dizziness
Menstrual complaints in women

Diagnosis and Testing

The DAO value is determined through a blood draw. The blood serum is then analyzed in a laboratory for diamine oxidase enzyme activity. For a meaningful result, patients are advised to avoid histamine-rich foods and DAO-inhibiting medications for several days before the test. A histamine H2 receptor antibody test or a food diary may also help confirm the diagnosis.

Treatment and Management of a Low DAO Value

If a low DAO value is detected, several therapeutic approaches are available:

Low-histamine diet: Reducing intake of histamine-rich foods such as aged cheeses, red wine, salami, and canned fish can significantly relieve symptoms.
DAO enzyme supplements: Dietary supplements containing diamine oxidase can be taken before histamine-rich meals to support histamine breakdown in the gut.
Increasing cofactor intake: Ensuring adequate intake of vitamin B6, copper, and vitamin C may support the body's own DAO activity.
Antihistamines: In acute cases, antihistamines can be used to relieve symptoms.
Treating underlying conditions: If an intestinal disorder is impairing DAO production, it should be treated directly.

References

Maintz, L. & Novak, N. (2007): Histamine and histamine intolerance. American Journal of Clinical Nutrition, 85(5), 1185–1196. Available via PubMed.
Manzotti, G. et al. (2016): Serum diamine oxidase activity in patients with histamine intolerance. International Journal of Immunopathology and Pharmacology, 29(1), 105–111.
Reese, I. et al. (2017): Guideline on management of suspected adverse reactions to ingested histamine – Allergo Journal International, 26(2), 72–79.

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