Diamine Oxidase Test
Why Test for Diamine Oxidase (DAO)?
Histamine intolerance is defined by an imbalance of histamine and the histamine degrading enzyme diamine oxidase (DAO), which is mainly produced in the small intestine.
A cause of histamine intolerance (HIT) may be drugs, which are inhibitors of the diamine oxidase. Alcohol and its degradation product acetaldehyde are inhibitors too. Additionally yet unknown effects on the activation of isoforms may have influence on the histamine-degrading capacity.
The typical symptoms of histamine intolerance are headache, diarrhea, migraine, engorged or dripping nose and especially in connection with food incorporation asthma and arrhythmia, hypotension, urticaria and dysmenorrhoea. Those with anaphylactic reactions often also have lower histamine activity. The diagnosis of histamine intolerance is achieved by determination of the diamine oxidase activity in serum.
Following a histamine-free diet normally results in a significant reduction or even disappearance of the symptoms within a few weeks.
The diagnosis of histamine intolerance based on the activity of diamine oxidase hence is only admissible when the activity is low. Nevertheless, when normal DAO activity and simultaneously increased histamine-levels are found, symptoms of histamine intolerance may be present. Especially after extreme histamine exposure like an anaphylactic shock increased activity of diamine oxidase and elevated histamine levels were measured.
Therefore the interpretation of the diamine oxidase activity always has to be done in context. If DAO is low, this constitutes diamine oxidase deficiency. However, if DAO is normal with a high histamine, this also indicates an insufficiency which will trigger symptoms.
Patients suffering from diseases like Urticaria, Crohns or Celiac Disease are reported to show low DAO activity in serum or plasma.
Furthermore DAO is described as marker for the status of the gut mucosa. Patients with chronic gut failure often show have reduced DAO values.