Histamine intolerance is defined by an imbalance of histamine and the histamine degrading enzyme diamine oxidase, which is mainly produced in the small intestine.
The present clinical experiences show that histamine intolerance is not congenital, but rather an acquired disease.
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 bronchiale and arrhythmia, hypotension, urticaria and dysmenorrhoea.
The diagnosis of histamine intolerance is achieved by thorough anamnesis and by the determination of the diamine oxidase activity in plasma or serum.
Following a histamine-free diet normally results in a significant reduction or even disappearance of the symptoms within a few weeks.
Because of the increased operation risk of histamine intolerant patients and the typical intolerance to roentgen contrast agent (histamine-liberator) and antirheumatica, histamine intolerance, which has a prevalence of 2-3% of the population, must be of special interest for all physicians. Especially anaphylactic shocks after bites from wasps or bees are often observed in combination with histamine intolerance.
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 with thorough anamnesis of the patients. A systematic provocation with histamine in a clinically controlled environment can give more details on the ability of the organism in degrading histamine. However, a time-course of DAO-activity gives best data for the diagnosis of histamine intolerance.
Patients suffering from diseases like Urticaria, Morbus Crohn 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.