Background Diamine Oxidase (DAO) has an essential role for degradation of exogenous histamine in the intestine; thus, histamine intolerance (HI) mainly has been correlated to a low concentration and/or activity of this enzyme. The objective of the study was to standardize a colorimetric technique to measure the enzymatic activity (function) of hDAO to then apply it to a series of 22 patients with a clinical diagnosis of HI. Methods For the standardization variables such as volume and type of sample, incubation time, wavelength of maximum absorption, types of substrates, and concentration of oxidized ascorbate were evaluated. Then the activity and concentration of DAO was determined in 22 patients diagnosed with HI and 22 healthy subjects. Results The mean of serum DAO concentration in the 22 patients was of 9.268 ± 1.124 U/mL. The mean of serum DAO concentration in the 22 controls was of 20.710 ± 2.509 U/mL, being significantly higher (P value 0.0002) the mean of the samples. The mean of serum DAO activity of the patients was of 1.143 ± 0.085 U/L and the controls was 1.533 ± 0.119 U/L, significantly greater than the patients (P value 0.011). In addition, the sensitivity of both techniques was 0.63. In the measuring of DAO concentration the specificity was 0.9, constituting a good diagnostic test, especially to rule out the true negatives. The determination of DAO activity had a specificity of 0.68. Conclusions Although we used a small number of patients and controls and the absorbance values were lower than expected, statistically significant differences were found in the levels of concentration and DAO activity between the patients with histamine intolerance and the controls. Therefore, the measuring of DAO concentration and DAO activity is a good diagnostic strategy for study suspect cases of HI. The simultaneous use of both assays allows to reduce positive and negative false results, for example, patients with normal DAO levels that could present a dysfunction in the activity of this enzyme.

Introduction. Histamine intolerance (HIT) is a pathology with an estimated prevalence of 1% in which there is an imbalance between the intake of histamine via the digestive tract and the body's ability to degrade it. This results in an excessive accumulation of histamine that determines the appearance of gastrointestinal, skin, respiratory and neurological symptoms. The enzyme responsible for degrading histamine in the extracellular space is diamine oxidase (DAO); therefore, HIT is caused due to a deficit in the concentration and/or in the activity of this enzyme. Because histamine is the main mediator of the classic symptoms of IgE-mediated allergic reactions, it is difficult to differentiate a true allergy from HIT since it has basically the same clinical manifestations. Objectives. The objective of this study was to perform a clinical characterization of patients with HIT and to determine the usefulness of quantifying serum DAO concentration in the diagnosis of HIT. Method: Twenty-two patients over the age of 18 with a history of histamine intolerance were recruited, in whom IgE-mediated food allergy was ruled out, and 22 healthy patients. Both groups were surveyed and serum DAO concentration was determined. Results: Middle-aged women predominated in the population with HIT. They described a wide variety of symptoms, with a dominance of abdominal pain, bloating, diarrhea, flushing, urticaria, itching, headache and dysmenorrhea. When comparing the average serum DAO concentration in the population with HIT (10.686 U/ml) with the average obtained in the control population (20.664 U/ml), there was a significant difference (p < 0.003). Conclusion. The determination of serum DAO concentration is a useful tool for the diagnosis of HIT.