Guideline on management of suspected adverse reactions to ingested histamine: Guideline of the German Society for Allergology and Clinical Immunology (DGAKI), the Society for Pediatric Allergology and Environmental Medicine (GPA), the Medical Association of German Allergologists (AeDA) as well as the Swiss Society for Allergology and Immunology (SGAI) and the Austrian Society for Allergology and Immunology (ÖGAI)

Measurement of diamine oxidase (DAO) during low-histamine or ordinary diet in patients with histamine intolerance

BACKGROUND/OBJECTIVES

Quantification of diamine oxidase (DAO) concentrations in serum has been proposed as an adjunctive diagnostic modality for the evaluation of histamine intolerance (HIT). Limited empirical data exist concerning the influence of dietary patterns on DAO levels.

SUBJECTS/METHODS

In the context of a prospective study employing a crossover design, 18 individuals diagnosed with HIT were randomized to initiate either a low histamine diet (LHD) or a conventional mixed diet (MXD). Serum DAO concentrations were measured at the commencement of the study and following each dietary phase. A control group underwent analogous DAO assessments without imposition of dietary constraints.

RESULTS

During the time when a diet restricted in histamine was implemented, noticeable differences in changes in DAO levels did not become apparent when compared to the changes observed during the mixed (MXD) phase. Specifically, among the group, 10 of the 18 patients exhibited elevated DAO values subsequent to the LHD regimen, while the remaining eight displayed either reduced or unchanging DAO levels. The prevalence of elevated DAO levels in the LHD group did not differ significantly from that observed in the control group during the MXD phase. Additionally, during the LHD phase, patients reported a significant reduction in gastrointestinal and cutaneous symptoms.

CONCLUSIONS

This prospective investigation underscores the enduring utility of a histamine-restricted diet, coupled with structured dietary reintroduction, as an efficacious diagnostic approach for individuals presenting with suspected food-related histamine hypersensitivity. Notably, the measurement of DAO levels appears to furnish only a limited capacity to discern dietary-induced fluctuations. Notwithstanding, the dynamics of DAO alteration do not appear to exhibit a discernible association with specific dietary patterns, a finding consistent across both patient and control groups.

Postprandial symptoms in disorders of gut-brain interaction and their potential as a treatment target

Postprandial, or meal-related, symptoms, such as abdominal pain, early satiation, fullness or bloating, are often reported by patients with disorders of gut-brain interaction, including functional dyspepsia (FD) or irritable bowel syndrome (IBS). We propose that postprandial symptoms arise via a distinct pathophysiological process. A physiological or psychological insult, for example, acute enteric infection, leads to loss of tolerance to a previously tolerated oral food antigen. This enables interaction of both the microbiota and the food antigen itself with the immune system, causing a localised immunological response, with activation of eosinophils and mast cells, and release of inflammatory mediators, including histamine and cytokines. These have more widespread systemic effects, including triggering nociceptive nerves and altering mood. Dietary interventions, including a diet low in fermentable oligosaccharides, disaccharides, monosaccharides and polyols, elimination of potential food antigens or gluten, IgG food sensitivity diets or salicylate restriction may benefit some patients with IBS or FD. This could be because the restriction of these foods or dietary components modulates this pathophysiological process. Similarly, drugs including proton pump inhibitors, histamine-receptor antagonists, mast cell stabilisers or even tricyclic or tetracyclic antidepressants, which have anti-histaminergic actions, all of which are potential treatments for FD and IBS, act on one or more of these mechanisms. It seems unlikely that food antigens driving intestinal immune activation are the entire explanation for postprandial symptoms in FD and IBS. In others, fermentation of intestinal carbohydrates, with gas release altering reflex responses, adverse reactions to food chemicals, central mechanisms or nocebo effects may dominate. However, if the concept that postprandial symptoms arise from food antigens driving an immune response in the gastrointestinal tract in a subset of patients is correct, it is paradigm-shifting, because if the choice of treatment were based on one or more of these therapeutic targets, patient outcomes may be improved.

Placebo-Controlled Histamine Challenge Disproves Suspicion of Histamine Intolerance

BACKGROUND

Histamine intolerance (HIT) is frequently diagnosed in patients with polysymptomatic otherwise unexplained symptoms.

OBJECTIVES

To exclude HIT by a single-blind placebo-controlled histamine challenge (SBPCHC), to study clinical features of patients with positive challenge, and to examine the predictability of HIT by biomarkers.

METHODS

SBPCHC was performed in 59 patients with suspected HIT. History and clinical data, including serum diamine oxidase (DAO) and histamine skin test wheal size of patients with positive versus negative SBPCHC, were compared.

RESULTS

Patients were predominantly middle-aged women (84.7%). Three-quarters reported improvement but never resolution of symptoms during a histamine-low diet. Histamine provocation was safe; only 1 patient was treated with antihistamines. Thirty-seven patients (62.7%) displayed symptoms to placebo. HIT was excluded in 50 patients (84.7%). Objective symptoms occurred in 4 of 59 cases (6.8%) after histamine but not after placebo challenge. These were diagnosed with "plausible HIT" because reactions occurring by chance could not be excluded. Another 5 patients (8.5%) were diagnosed with "possible HIT" after case-dependent detailed analysis. Patients with plausible/possible HIT had reported more gastrointestinal symptoms (P = .01), but comparable diet response and equal histamine skin prick test wheal sizes to those without HIT. Serum DAO activity tended to be lower in patients with HIT (P = .08), but was highly variable in those without, limiting its value as a biomarker.

CONCLUSIONS

SBPCHC disproves HIT in the majority of patients. Placebo-controlled challenges are needed as placebo reactions were frequent. Gastrointestinal symptoms after food intake and reduced DAO levels are markers for HIT; however, specificity is not sufficient enough for making the diagnosis.

Myths and Facts about Food Intolerance: A Narrative Review

Most adverse reactions to food are patient self-reported and not based on validated tests but nevertheless lead to dietary restrictions, with patients believing that these restrictions will improve their symptoms and quality of life. We aimed to clarify the myths and reality of common food intolerances, giving clinicians a guide on diagnosing and treating these cases. We performed a narrative review of the latest evidence on the widespread food intolerances reported by our patients, giving indications on the clinical presentations, possible tests, and dietary suggestions, and underlining the myths and reality. While lactose intolerance and hereditary fructose intolerance are based on well-defined mechanisms and have validated diagnostic tests, non-coeliac gluten sensitivity and fermentable oligosaccharide, disaccharide, monosaccharide, and polyol (FODMAP) intolerance are mainly based on patients' reports. Others, like non-hereditary fructose, sorbitol, and histamine intolerance, still need more evidence and often cause unnecessary dietary restrictions. Finally, the main outcome of the present review is that the medical community should work to reduce the spread of unvalidated tests, the leading cause of the problematic management of our patients.

A personalized management approach in disorders of the irritable bowel syndrome spectrum

Symptoms of the disorders across the irritable bowel syndrome (IBS) spectrum include several different, usually postprandial, abdominal complaints. Up to date, dietary treatments of the IBS have neither been personalized nor diagnosed with sufficient scientific evidence. They have mostly been treated using 'one-size-fits-all' approaches. Such include exclusion diets, a low fermentable oligosaccharides, disaccharides, monosaccharides and polyols diet, and gluten-free diets, lactose-free diets, a diet recommended by the UK National Institute for Health and Care Excellence, and a wheat-free diet. The exact pathophysiology of IBS disorders across the spectrum is still unclear. However, the symptom profile of IBS spectrum disorders seems similar to that of food intolerance/malabsorption syndromes. Celiac disease, fructose malabsorption, histamine intolerance and lactose intolerance represent food intolerance/malabsorption disorders based on the indigestion of sugars and/or proteins. Helicobacter pylori infection may potentially promote the development of IBS and, when facing a case of IBS-like symptoms, a search for intolerance/malabsorption and H. pylori should be added to find the correct treatment for the respective patient. This review will discuss why the 'one-size-fits-all' dietary approach in the treatment of complaints across the IBS spectrum cannot be successful. Hence, it will provide an overview of the most common overall dietary approaches currently used, and why those should be discouraged. Alternatively, a noninvasive diagnostic workup of the pathophysiologic factors of food intolerance/malabsorption in each patient with symptoms of the IBS spectrum is suggested. Additionally, if H. pylori is found, eradication therapy is mandatory, and if food intolerance/malabsorption is detected, an individual and personalized dietary intervention by a registered dietician is recommended.

Functional Abdominal Pain Disorders in Children May Be Associated with Food Intolerance/Malabsorption

Functional abdominal pain disorders (FAPDs) are among the most common types of chronic pain disorders in children. FAPD symptoms are characterized by chronic abdominal pain and changed bowel movements. The pathophysiology of FAPDs in children is unknown, but these conditions may have an imprecise clinical overlap to food intolerance/malabsorption. We report on 51 consecutive children (23/28 males/females; median age 15.3 years) with investigated FAPDs from 2017 to 2022 in this retrospective pilot study. Small intestinal biopsies in children demonstrated the association of lactase and diamine oxidase (DAO), which prompted us to perform hydrogen (H2) breath tests for lactose intolerance (LIT) and determine serum DAO for the evaluation of histamine intolerance (HIT) in pediatric patients with FAPDs. To complete the food intolerance/malabsorption evaluation tests, we included a search for antibodies against tissue transglutaminase to find celiac disease (CD), performed H2 breath tests to detect fructose malabsorption (FM), and conducted a search for IgA antibodies against H. pylori infection. The results demonstrate that all 51 children evaluated were diagnosed with food intolerance/malabsorption and/or various combinations thereof. Seven children showed FM, eight of the children had HIT, and eight children had LIT. The other children had combinations: thirteen children (25.5%) had HIT and LIT, seven children (9.8%) had FM with HIT, five children (13.7%) had FM and LIT, and three children (5.9%) had a triple combination of FM, HIT, and LIT. By describing this method of personalized investigation for food intolerance/malabsorption in children with FAPDs, we demonstrate that functional abdominal pain disorders may be associated with food intolerance/malabsorption. After such diagnosis in this pediatric population, a registered dietitian helped to establish a reduction and/or exclusion diet individually tailored to their symptomatology.

[Principles of allergy diagnostics]

BACKGROUND

Allergies are frequent and approximately 30% of the general population in Germany are affected. The specific sensitization against an allergen is asymptomatic. On renewed allergen contact the symptoms are indicative of the underlying pathomechanism. A variety of different test procedures are available to identify allergic reactions.

OBJECTIVE AND AIM

In this review article the typical clinical symptoms of allergic reactions are assigned to mechanisms and possible test methods are presented and discussed. Current developments in recombinant serum diagnostics and cellular testing methods are presented.

Histamine intolerance

Histamine intolerance (HIT) is a non-immunological disorder associated with an impaired ability to metabolize ingested histamine. Manifestation of HIT includes gastrointestinal and non-gastrointestinal symptoms. Clinical symptoms of HIT are non-specific and can imitate different diseases such as allergies, food intolerance, mastocytosis and other. The diagnosis of HIT is difficult. There are several candidate tests to detect DAO insufficiency, but their informative value is questionable. Currently, a positive clinical effect of a low-histamine diet is the most important for establishing the diagnosis. Equally in the treatment, a low-histamine diet is the most crucial approach. Other therapeutic options such as DAO supplementation treatment with antihistamines or probiotics are considered as complementary treatments. Our article provides a review on histamine intolerance, focusing on etiology and the diagnostic and treatment possibilities.

Advances in the Clinical Application of Histamine and Diamine Oxidase (DAO) Activity: A Review

The serum level of diamine oxidase (DAO) reflects the integrity and maturation of the small intestinal mucosa. This measure is important in diagnosing various diseases, including chronic urticaria tachyphylaxis, multiple organ dysfunction syndrome, preterm abortion, and migraine. This review aimed to summarize the findings of previous studies on the changes in DAO levels in diverse diseases and the application of this enzyme in the clinical setting, as well as the roles of this enzyme under physiological and pathological conditions. The advances in the mechanism and clinical application of DAO presented in this review will contribute to a better understanding of this enzyme and open up new and broader perspectives for future basic research and clinical applications.

1-methylhistamine as a potential biomarker of food histamine intolerance. A pilot study

Efforts are currently being directed to identify a non-invasive marker that can serve as a solid and clinically irrefutable diagnostic criterion for histamine intolerance associated with diamine oxidase (DAO) deficiency. Accordingly, the identification of biomarkers of histamine (HA) metabolism in urine is proposed as a possible new diagnostic strategy. It is hypothesized that individuals with histamine intolerance could have a different urinary profile of HA and its metabolites in comparison with the healthy population. Thus, the aim of this study was to assess the urinary excretion of HA and 1-methylhistamine (MHA) in individuals diagnosed with histamine intolerance and in a control group. Levels of HA and MHA were compared between 24 h and first morning spot urine in a subgroup of 14 control individuals. Then, HA and MHA concentrations in spot urine of 32 histamine intolerant and 55 control individuals were determined by ultra-high performance liquid chromatography and fluorometric detection (UHPLC-FL) and normalized by creatinine. No differences were found between HA and MHA levels in 24 h and first morning samples. Overall, histamine intolerant patients presented a distinct urinary excretion profile compared to the control group due to lower levels of MHA. No differences in urinary MHA were observed related to serum DAO activity. Spot urine samples were thus validated as a reliable tool to determine the urinary excretion of HA and MHA. These results constitute a starting point for the study of HA metabolomics as a suitable and non-invasive approach to histamine intolerance diagnosis.

Recent advances in the application of microbial diamine oxidases and other histamine-oxidizing enzymes

The consumption of foods fraught with histamine can lead to various allergy-like symptoms if the histamine is not sufficiently degraded in the human body. The degradation occurs primarily in the small intestine, naturally catalyzed by the human diamine oxidase (DAO). An inherent or acquired deficiency in human DAO function causes the accumulation of histamine and subsequent intrusion of histamine into the bloodstream. The histamine exerts its effects acting on different histamine receptors all over the body but also directly in the intestinal lumen. The inability to degrade sufficient amounts of dietary histamine is known as the ‘histamine intolerance’. It would be preferable to solve this problem initially by the production of histamine-free or -reduced foods and by the oral supplementation of exogenous DAO supporting the human DAO in the small intestine. For the latter, DAOs from mammalian, herbal and microbial sources may be applicable. Microbial DAOs seem to be the most promising choice due to their possibility of an efficient biotechnological production in suitable microbial hosts. However, their biochemical properties, such as activity and stability under process conditions and substrate selectivity, play important roles for their successful application. This review deals with the advances and challenges of DAOs and other histamine-oxidizing enzymes for their potential application as processing aids for the production of histamine-reduced foods or as orally administered adjuvants to humans who have been eating food fraught with histamine.

Histamine intolerance (HIT)

Histamine intolerance (HIT) is food intolerance of non-immunological origin, and it results from an imbalance between the consumption of histamine with food and the organism ability to metabolize it. The patients with HIT were found to have a significantly reduced concentration of histamine-degrading enzymes, diamine oxidase (DAO) and histamine N-methyltransferase (HNMT). Factors which have been identified that are conducive to histamine intolerance are:  genetic factors, dysbacteriosis, chronic diseases – especially allergic and intestinal diseases, chronic infections, mastocytosis and some drug use. Clinical symptoms of histamine excess may affect various organs and systems - the most common are skin symptoms (pruritis, erythema) nausea, vomiting, abdominal pain, diarrhea, headaches and sometimes severe reactions with shortness of breath, arrhythmias, blood pressure drop, and even cardiac arrest. Diagnostic methods in HIT utilize determination of serum DAO, determination of histamine metabolites in urine, measurement of the histamine wheal in the 50th minute of the skin prick test (SPT), gastroscopy with intestinal biopsy, diagnostic and therapeutic test, oral histamine-challenge test and genetic tests. The mainstay of histamine intolerance treatment if a low-histamine diet. Patients should avoid products belonging to the three groups of food: containing large amounts of histamine, histamine liberators, and products inhibiting the activity of DAO. Additionally, supplements containing DAO and antihistamines can be used.

Serum Diamine Oxidase Values, Indicating Histamine Intolerance, Influence Lactose Tolerance Breath Test Results

Lactose intolerance (LIT) is one of the major causes of irritable bowel syndrome (IBS) spectrum complaints. Differences in inadequate lactose digestion are described as various LIT phenotypes with basically unknown pathophysiology. In LIT patients, we retrospectively assessed the effect of histamine intolerance (HIT) on expiratory hydrogen (H2) during H2 lactose breath tests. In a retrospective evaluation of charts from 402 LIT patients, 200 patients were identified as having only LIT. The other 202 LIT patients were found to additionally have diamine oxidase (DAO) values of <10 U/mL, which indicates histamine intolerance (HIT). To identify HIT, standardized questionnaires, low serum DAO values and responses to a histamine-reduced diet were used. Patients were separated into three diagnostic groups according to the result of H2 breath tests: (1) LIT, with an H2 increase of >20 parts per million (ppm), but a blood glucose (BG) increase of >20 mg/dL, (2) LIT with an H2 increase of 20 ppm in combination with a BG increase of <20 mg/dL, and (3) LIT with an exhaled H2 increase of <20 ppm and BG increase of <20 mg/dL. Pairwise comparison with the Kruskal Wallis test was used to compare the areas under the curve (AUC) of LIT and LIT with HIT patients. Exhaled H2 values were significantly higher in H2 > 20 ppm and BG < 20 mg/dL patients with LIT and HIT (p = 0.007). This diagnostic group also showed a significant higher number of patients (p = 0.012) and a significant higher number of patients with gastrointestinal (GI) symptoms during H2 breath tests (p < 0.001). Therefore, low serum DAO values, indicating HIT, influence results of lactose tolerance breath tests.

Basal Serum Diamine Oxidase Levels as a Biomarker of Histamine Intolerance: A Retrospective Cohort Study

Background: Histamine Intolerance (HIT) is a multifaceted pseudoallergic disorder possibly due to defective histamine metabolism. Diamine oxidase (DAO) contributes to histamine degradation and can be measured in the serum. The role of DAO measurement in the diagnostic work-up of HIT still remains unclear, and conflicting results have been reported in the literature. Therefore, we aimed to evaluate the possible clinical usefulness and consistency of DAO value ranges as provided by the assay manufacturer and verify whether they could predict the response to treatment. Methods: We retrospectively analyzed 192 outpatients with HIT symptoms and measured serum DAO values at baseline. Patients were prescribed either with low-histamine diet and/or enzymatic supplementation according to symptom severity and re-evaluated six to eight months later. Patients were stratified into three groups according to DAO levels: <3 U/mL, 3−10 U/mL, and >10 U/mL. HIT severity was assessed on a scale of 1 to 5 before and after treatment. Results: A total of 146 patients completed the study. Gastrointestinal and cutaneous symptoms, often associated with headache, were more frequent in subjects with DAO < 10 U/mL. Symptom severity and DAO ranges were correlated. Patients with intermediate DAO levels (3−10 U/mL) showed a more complex clinical phenotype but also a more significant improvement in symptom severity (score reduction 50%, interquartile range (IQR) = 33−60%) when compared to patients with low DAO (40%, IQR = 20−60%; p = 0.045) or high DAO (33%, IQR = 0−50%; p < 0.001). Complex clinical phenotypes were also more frequent in patients with intermediate DAO levels. Conclusions: HIT is characterized by typical symptoms and low levels of DAO activity. Symptom severity was associated with the degree of DAO deficiency. Patients with DAO values between 3 and 10 U/mL show the best response to treatment (low-histamine diet and/or DAO supplementation). DAO value could arguably be considered as a predictor of clinical response to treatment. Prospective studies are needed to confirm these data.

Histamine Intolerance-A Kind of Pseudoallergic Reaction

Histamine intolerance (HIT) is a common disorder associated with impaired histamine metabolism. Notwithstanding, it is often misdiagnosed as other diseases because of its lack of specific clinical manifestations. HIT did not gain traction until the early 21st century. In this review, we will focus on the latest research and elaborate on the clinical manifestations of HIT, including its manifestations in special populations such as atopic dermatitis (AD) and chronic urticaria (CU), as well as the latest understanding of its etiology and pathogenesis. In addition, we will explore the latest treatment strategies for HIT and the treatment of specific cases.

Helicobacter pylori infection and lactose intolerance increase expiratory hydrogen

Infection with Helicobacter pylori (H.pylori) may cause dyspepsia and/or unexplained functional nonspecific, gastrointestinal complaints of the irritable bowel syndrome (IBS) spectrum. Hitherto, in H. pylori infected patients with symptoms of the IBS spectrum the occurrence of additional food intolerance/malabsorption is not evaluated. We used a retrospective analysis of charts from 548 patients who presented with gastrointestinal complaints of the irritable bowel syndrome spectrum. An enzyme-linked IgA immunosorbent assay or histologic evaluation of gastric mucosa were used to detect H. pylori infection. A hydrogen breath (H₂) test was performed to evaluate fructose malabsorption (FM) and lactose intolerance (LIT). Serum diamine oxidase value of <10 U/ml and a response to a histamine-reduced diet was used to identify histamine intolerance (HIT). We found 293 patients infected with H. pylori, within these were 58 H. pylori patients with LIT, 23 H. pylori LIT patients with FM and 46 H. pylori LIT patients with HIT. Additionally, 13 H. pylori, lactose- and histamine intolerance patients also had FM. The Kruskal Wallis test and pairwise comparison were used to analyze differences of the area under the curve of expiratory hydrogen. In lactose H₂ breath tests compared with LIT-only patients, LIT with H. pylori, LIT and H. pylori with HIT, LIT and H. pylori with FM showed significantly higher exhaled H₂ levels (p=0.022). Pairwise comparison demonstrated H. pylori infected patients with LIT exhaled more H₂ compared to LIT-only (p=0.029). H. pylori with lactose- and histamine intolerance, and H. pylori with lactose-, histamine intolerance and FM compared to H. pylori-only patients indicated a significantly higher occurrence of stomach pain during lactose H₂ breath tests (p=0.012 and p=0.005, respectively). We demonstrate that LIT patients with high expiratory H₂ levels in lactose breath tests may have H. pylori infection and possibly additional food intolerance/malabsorption. Subsequently, besides H. pylori eradication, a dietician is necessary for an individually tailored reduction- or exclusion diet of symptom triggering food components.