Histamine Clearance Index
A Targeted Histamine Intolerance Test
The Histamine Clearance Index™ (HCI) is a histamine intolerance test that facilitates the clinical evaluation of histamine metabolism and clearance capacity.
Understanding histamine intolerance starts with understanding how the body breaks down histamine.
Documents
Explore our Histamine Clearance Index educational resources. Learn how histamine clearance is assessed and how impaired histamine metabolism may influence patient symptoms.
Clinical Information
What Is Histamine Intolerance?
When histamine levels surpass the body’s capacity for degradation and elimination, patients may experience what is commonly referred to as histamine intolerance.
Histamine is a naturally occurring biogenic amine formed from the amino acid histidine. It plays important roles in digestion, immune signaling, and neurological function. However, when histamine is not broken down efficiently, it can accumulate in the body and trigger a range of allergy-like responses without an underlying immune-mediated allergy.
The body relies primarily on the enzyme diamine oxidase (DAO) to break down histamine. When DAO activity is impaired, histamine elimination slows, and symptoms may occur.
The Role of Diamine Oxidase (DAO) in Histamine Metabolism
DAO is the key enzyme responsible for histamine degradation, particularly histamine consumed through food or exposed within the gut.
Histamine intolerance may arise when:
- DAO activity is reduced
- DAO function is inhibited
- Histamine levels exceed the body’s capacity for elimination
- Excess histamine levels are produced from the gut microbiome
Why the Histamine Clearance Index Matters
The Histamine Clearance Index helps evaluate impaired histamine elimination, which may occur as a result of reduced DAO activity. By assessing the functional capacity of DAO, the Histamine Clearance Index offers deeper clinical insight than standalone measurements of histamine or DAO levels.
Impaired histamine breakdown can occur for two primary reasons:
DAO Inhibition
DAO production may be normal, but enzyme activity is reduced, leading to elevated histamine. This is often influenced by external factors such as medications, alcohol, or other inhibitors.
DAO Deficiency
DAO levels are reduced, limiting the body’s ability to break down histamine. This may be associated with genetic polymorphisms or underlying gastrointestinal and inflammatory conditions.
Which Patients Can Benefit from Testing the Histamine Clearance Index?
Patients experiencing a wide range of allergy-like or unexplained symptoms, particularly those that worsen after eating histamine-rich foods, may benefit from an assessment of histamine clearance. Common symptoms include:
- Bloating, abdominal pain, diarrhea, constipation, or nausea
- Headaches or migraines
- Flushing, itching, hives, or skin rashes
- Nasal congestion or runny nose
- Rapid heart rate or palpitations
- Dizziness or lightheadedness
- Anxiety or sleep disturbances
How the Histamine Clearance Index Evaluates Histamine Intolerance
The Histamine Clearance Index helps clarify:
- Whether histamine clearance is impaired
- Why histamine symptoms may persist despite dietary modification
Interpreted alongside clinical context, this information supports more precise interpretation in patients with suspected histamine intolerance, multisystemic symptoms, or unexplained histamine reactivity.
Optimize Outcomes With the Histamine Clearance Index Test
Histamine Clearance Index Frequently Asked Questions (FAQs)
What is histamine intolerance?
Histamine intolerance occurs when histamine levels exceed the body’s ability to break it down and eliminate it efficiently. Histamine is a naturally occurring compound involved in digestion, immune responses, and nervous system signaling. Under normal circumstances, enzymes—primarily diamine oxidase (DAO)—help degrade histamine from food and external sources.
When histamine clearance is impaired, histamine can accumulate in the body and contribute to a range of symptoms that often resemble allergic reactions. These may include digestive discomfort, headaches, flushing, skin reactions, nasal congestion, dizziness, or sleep disturbances. Histamine intolerance is not a true allergy but rather reflects an imbalance between histamine production, intake, and the body’s capacity to degrade it.
What is a histamine intolerance test?
A histamine intolerance test helps evaluate whether symptoms are related to impaired histamine breakdown rather than a true allergy. The Histamine Clearance Index™ assesses how effectively the body eliminates histamine.
Who should consider a histamine intolerance test?
Patients with allergy-like or multisystem symptoms – such as digestive discomfort, headaches, flushing, or unexplained reactions to histamine‑rich foods – may benefit from histamine intolerance testing.
What causes histamine intolerance?
Histamine intolerance may occur when histamine levels exceed the body’s capacity for breakdown, which may be due in part to reduced diamine oxidase (DAO) enzyme levels, DAO inhibition, or insufficient DAO levels.
How is the Histamine Clearance Index different from standard DAO or histamine testing?
Standard testing measures histamine or DAO levels. While this can be useful, it does not always reflect how effectively histamine is being broken down in the body.
The Histamine Clearance Index evaluates the functional capacity of DAO — providing a more clinically relevant view of how well histamine is being cleared.
Can histamine intolerance exist without a true allergy?
Yes. Histamine intolerance involves impaired histamine metabolism and can result in allergy-like symptoms without an immune-mediated allergic response.
Why do histamine symptoms persist despite dietary changes?
In some patients, symptoms persist because histamine breakdown remains impaired even with dietary modification, highlighting the importance of evaluating underlying histamine metabolism.
What is the IgG Food Explorer test used for?
The IgG Food Explorer is a food sensitivity test that measures IgG antibody responses to over 250 food antigens. It helps identify delayed immune reactions to foods that may be contributing to inflammation, digestive issues, skin conditions, headaches, and other chronic symptoms.
Test Ordering Options
Test Name: HCI - Histamine Clearance Index™
Methodology: ELISA
Sample Type: Whole blood
If you already have an account with us, you may order through our online Practitioner Portal accessible at the top of this page.
Tests That May Complement the Histamine Clearance Index
The Histamine Clearance Index provides insight into histamine metabolism and DAO-related dysfunction. Depending on the clinical presentation, additional testing may help further contextualize findings:
- GI-MAP (Microbial Assay Plus) – May be considered to evaluate gastrointestinal contributors to impaired histamine metabolism, including dysbiosis, overgrowth of histamine-producing organisms, intestinal inflammation, and gut barrier disruption that can influence histamine production and degradation.
- IgE Allergy Explorer™ – May be used to evaluate immune-mediated allergic responses and help differentiate true IgE-mediated allergy from histamine intolerance.
- Organic Megabolomics (OMX®) – May provide insight into histidine metabolism and related biochemical pathways that can contribute to histamine burden, as well as broader metabolic patterns relevant to multisystem symptoms.