Abstract: A method for diagnosing histamine intolerance syndrome in a patient suspected of suffering from insufficient histamine inactivation activity. The diagnostic procedure involves spiking or administering of histamine labelled with a stable isotope. Samples (usually serum, plasma, urine) are taken after one or more predetermined periods of time and an aprotic solvent is added to remove proteins and organic salts. The amounts of isotopically labelled histamine in the samples and, if applicable, one or more isotopically labelled inactivation products of histamine are determined by hydrophilic interaction chromatography and mass spectrometry. The histamine inactivation activity can then be determined from the amounts and ratios of isotopically labelled histamine, imidazole acetic acid, and methylhistamine, and optionally methylimidazole acetic acid. Diagnosis is based on the comparison with the histamine inactivation found in healthy individuals.

Abstract: A method of diagnosis of histamine intolerance in a person suspected of suffering from histamine intolerance syndrome. Isotope-labeled histamine metabolites, namely imidazole acetic acid and methylimidazole acetic acid are identified and measured in serum, plasma, urine and other bodily fluids following derivatization with a hydrazinoquinoline derivatization agent using the LC-MS/MS technique. The method and analytical technique is very sensitive and allows a safe use of an isotope-labeled oral histamine load as well as time-dependent measurements of the total activity of secreted and membrane-associated DAO enzymes for the sake of a differential diagnosis of histamine intolerance syndrome compared to food allergy, food hypersensitivity or food intolerance.