Quantitative measurement of diamine oxidase (DAO) enzyme concentration from dried blood spot by ELISA for assessment of histamine intolerance and DAO deficiency.
Diamine Oxidase (DAO)
3–5 working days
This method quantifies diamine oxidase (DAO) enzyme concentration from a dried blood spot to assess histamine intolerance and DAO deficiency. DAO is the primary enzyme responsible for degrading dietary histamine in the gastrointestinal tract. Low DAO activity or concentration permits histamine to accumulate systemically, leading to delayed pseudo-allergic reactions despite negative conventional allergy testing.
Clinical indications for DAO measurement include:
Estimated prevalence of DAO deficiency is 1–3% of the general population, making histamine intolerance a modifiable condition affecting a meaningful portion of patients presenting with non-allergic allergy-like symptoms. Diagnosis enables dietary modification and consideration of DAO supplementation, both of which can dramatically improve quality of life.
Histamine is an important signalling molecule synthesised from the amino acid L-histidine by histidine decarboxylase. While much of the body's histamine is produced endogenously (particularly by mast cells and basophils), additional histamine is acquired from dietary sources including aged cheeses, processed meats, fermented foods, certain wines, and other products with high biogenic amine content.
Estimated population prevalence of DAO deficiency, making it a common but often unrecognised condition
Symptoms mimic allergic reactions but conventional allergy tests are normal, leading to years of diagnostic uncertainty
Dietary restriction of high-histamine foods and DAO supplementation can produce rapid symptom resolution
Histamine is degraded via two principal enzymatic pathways: the primary pathway is mediated by diamine oxidase (DAO), a copper-dependent enzyme expressed throughout the gastrointestinal tract, particularly in the intestinal mucosa and the liver. The secondary pathway uses histamine N-methyltransferase (HNMT), which is expressed predominantly in the central nervous system and other tissues. When DAO activity is reduced, either from genetic factors, acquired enzyme suppression, or intestinal barrier compromise, histamine accumulates and enters systemic circulation.
Causes of DAO deficiency include: genetic polymorphisms and mutations affecting DAO expression or function; medications that suppress DAO activity (NSAIDs, antihistamines, cimetidine, certain antibiotics, alcohol); and acquired deficiency from intestinal inflammation, dysbiosis, or damage to the intestinal epithelium. Patients with inflammatory bowel disease, small intestinal bacterial overgrowth (SIBO), or celiac disease frequently develop acquired DAO deficiency because the inflammatory milieu suppresses enzyme expression and/or damages the intestinal mucosa that produces DAO.
The clinical manifestations of histamine intolerance are diverse and frequently mimic IgE-mediated allergic reactions but occur with a delay of 30 minutes to several hours after histamine ingestion. Common symptoms include migraine headaches, flushing and pruritus (skin itching), gastrointestinal symptoms (abdominal cramping, diarrhoea, nausea), nasal congestion or rhinorrhoea, and fatigue. Because these symptoms are delayed and variable in their presentation, histamine intolerance is frequently misattributed to true food allergies, idiopathic urticaria, or psychological causes.
| Classification | Range | Interpretation |
|---|---|---|
| Normal | >10 U/mL | Sufficient enzyme activity to metabolise dietary histamine |
| Reduced | 3–10 U/mL | May indicate histamine intolerance; symptoms possible after high-histamine meals |
| Deficient | <3 U/mL | Significant DAO deficiency; high probability of histamine intolerance symptoms |
| Sample Type | Normal Range |
|---|---|
| Plasma | <0.3 ng/mL |
| Whole blood | <1 ng/mL |
Elevated histamine combined with low DAO is the strongest indicator of histamine intolerance.
This ratio provides a more complete picture than either marker alone.
DAO activity can fluctuate based on hormonal status, medication use, gut health, and recent dietary histamine load. Your report includes detailed interpretation.
Histamine intolerance is an underdiagnosed condition where the body cannot break down histamine efficiently, leading to a wide range of symptoms that often mimic allergies or other conditions:
If your results indicate low DAO activity or elevated histamine, targeted dietary and supplemental strategies can significantly reduce symptoms:
Re-test DAO activity after 8–12 weeks of intervention. Many people see significant improvements once gut health is addressed and dietary triggers are managed.
Diamine oxidase is quantified from dried blood spots using enzyme-linked immunosorbent assay (ELISA). The method measures total DAO protein concentration via sandwich ELISA using monoclonal antibodies specific to human DAO. This approach quantifies the absolute amount of enzyme present, distinct from enzyme activity assays which measure catalytic function.
ELISA measurement of DAO concentration from DBS is advantageous because: it requires minimal sample volume from a convenient heel prick; DBS samples are stable at ambient temperature; and the semi-quantitative approach provides clear discrimination between normal and deficient DAO levels. Results are typically expressed in units per millilitre (U/mL) or as categorical classifications (normal, low-normal, deficient) based on reference ranges established in the healthy population.
Dried blood spot collection is ideal for DAO measurement. The sample is stable at room temperature and does not require special handling or rapid processing. DBS collection is suitable for all ages and enables convenient home or point-of-care testing, facilitating broad access to histamine intolerance assessment in clinical and wellness settings.
From enquiry to results in a few simple steps — no clinic visit required.
This test is available to healthcare professionals, wellness brands, clinics, and research institutions worldwide. We currently serve partners in:
Whether you need testing services for your patients, white-label kits for your brand, or method transfer to your own laboratory — get in touch to discuss how we can work together.
Histamine intolerance is a condition where the body cannot break down histamine efficiently, usually due to low activity or concentration of the diamine oxidase (DAO) enzyme. DAO is the primary enzyme responsible for degrading dietary histamine in the gastrointestinal tract. When DAO is insufficient, histamine accumulates systemically after eating histamine-rich foods, causing symptoms such as headaches, digestive issues, skin flushing, nasal congestion, and fatigue — often hours after eating.
This test measures the concentration of diamine oxidase (DAO) enzyme from a finger-prick dried blood spot using ELISA (enzyme-linked immunosorbent assay). Low DAO levels suggest a reduced capacity to degrade dietary histamine, which is the underlying mechanism of histamine intolerance. The test quantifies total DAO protein using monoclonal antibodies specific to human DAO.
The test uses a simple finger-prick to collect a few drops of blood onto a dried blood spot (DBS) card. You can do this at home or in a clinic — no venous blood draw is needed. The DBS sample is stable at room temperature and does not require special handling or rapid processing, making it suitable for convenient at-home collection and postal transit.
Results are typically delivered within 3 to 5 working days from the time your sample arrives at our laboratory. Results are expressed as DAO concentration units and categorised as normal, low-normal, or deficient based on reference ranges established in the healthy population.
Foods with high histamine content include aged cheeses, fermented foods such as sauerkraut, kimchi, and kombucha, cured and processed meats, smoked fish, wine (particularly red wine), beer, and vinegar. Some foods also trigger histamine release from mast cells even though they do not contain histamine directly — these include citrus fruits, tomatoes, shellfish, and strawberries. A low-histamine diet guided by DAO testing results can produce significant symptom improvement.
Masdiag's histamine DAO test is available worldwide through our partner network. We currently serve healthcare professionals, wellness brands, and clinics in Europe, the United Kingdom, Asia, Australia, New Zealand, and the United States. Contact us to discuss testing services, white-label kits, or method transfer to your laboratory.
Whether you need testing services, method transfer, or white-label kit development — we'd love to hear from you.