DAO Serum Levels

Serum DAO (Diamine Oxidase) can be measured via blood test and is used as a marker for Histamine Intolerance.

What It Tells You

Low serum DAO suggests reduced capacity to break down extracellular Histamine. This can result from:

• Genetic variants in the AOC1 gene (see DAO for specific SNPs)
• Gut inflammation damaging the enterocytes that produce DAO
• Medications that inhibit DAO (alcohol, NSAIDs, certain antibiotics)

Limitations

Serum DAO reflects circulating enzyme levels, not necessarily gut mucosal DAO activity. A person can have normal serum DAO but insufficient DAO at the intestinal wall (where it needs to act on Dietary Histamine). Conversely, low serum DAO confirms reduced capacity but doesn’t quantify how much dietary histamine actually gets through.

Reference ranges vary by lab. There is no universally agreed-upon cutoff for “deficient.” Many providers use it as supporting evidence alongside clinical history and dietary response, not as a standalone diagnostic.

When It’s Useful

Most informative when combined with clinical context: low serum DAO + symptom correlation with high-histamine meals + improvement on a low-histamine diet + genetic DAO variants = a strong case for Histamine Intolerance as a significant component.