Histamine intolerance (HIT) is characterized by an imbalance between histamine intake and the capacity for histamine degradation. The main enzyme for metabolizing ingested histamine is diamine oxidase (DAO). Determining DAO activity in serum may be useful in diagnosing HIT.
Over a period of 3.5 years we recruited 316 subjects with clinically suspected HIT and 55 healthy controls. Serum DAO activity was measured with a quantitative enzyme immunoassay. Twenty patients with highly reduced DAO activity went on a histamine-free diet for 6–12 months. Afterwards, their DAO activity was determined again.
We found that DAO activity was significantly lower in patients than in healthy control subjects (P < 0.0001). Furthermore, 54 patients had highly reduced serum DAO activity (< 40 HDU/ml). Their main symptoms involved the skin, gastrointestinal tract, respiratory system, and eyes. In all the 20 patients with highly reduced DAO activity, the main clinical symptoms typical of histamine intolerance disappeared after they adopted a histamine-free diet. Furthermore, the serum DAO activity values measured increased significantly (P < 0.0001).
Our results suggest that determining DAO activity in serum is a useful tool in diagnosing HIT. Furthermore, our results showed the benefit of a histamine-free diet because after the diet the majority of symptoms disappeared and the serum DAO activity significantly increased.