Diamine oxidase (DAO, histaminase) (Engl. diamine oxidase) is a copper-containing enzyme (it contains two copper atoms in the active site and has vitamin B6 as a cofactor) that can degrade histamine and other biogenic amines (such as; cadaverine, feruloylputresine, dopamine, phenethylamine/phenylethylamine, putrescine, serotonin, spermidine, spermine, synnephrine, tryptamine, tyramine, norepinephrine, etc.).
A deficiency of DAO is thought to lead to what is known as histamine intolerance: Individuals with non-immunologically mediated hypersensitivity to biogenic amines lack the enzyme necessary for amine degradation (diamine oxidase (DAO) concentration in the intestinal tract and histamine methyltransferase in the liver) or have an enzyme defect, respectively.
The procedure
Material needed
- EDTA plasma or blood serum
- Freshly collected samples (plasma or serum) must be centrifuged immediately after blood collection and kept refrigerated.
Preparation of the patient
- Not necessary
Disruptive factors
- DAO activity can be inhibited by substances such as alcohol or drugs (N-acetylcysteine, ambroxol, aminophylline, amitriptyline, chloroquine, clavulanic acid, isoniazid, metamizole, metoclopramide, propafenone, verapamil, and many others).
Normal values
| DAO activity | U/ml |
| Very low enzyme activity | < 3 |
| Mean enzyme activity | 3-10 |
| Normal enzyme activity | > 10 |
Indications
- Suspected histamine intolerance (pseudoallergies).
- Suspicion of DAO deficiency in inflammatory bowel disease or by activity-inhibiting substances (see above under interfering factors).
Interpretation
Interpretation of increased values
- Not relevant to disease
Interpretation of lowered values
- DAO deficiency
Other indications
- In histamine-intolerant patients, one very often finds, in addition to a lowered DAO activity and increased histamine levels, low vitamin B6 and copper levels.
- Alcohol decreases the enzyme activity of DAO (diamine oxidase) and increases the absorption of histamine!This leads simultaneously to a non-IgE-mediated release of histamine from the mast cells and basophilic granulocytes.
