Silver Bullet, or False Promise?
Understanding histamine intolerance is a complex process, so it's normal to want to look for a simple answer. Many people see histamine tests advertised online and think that they've found the silver bullet that will tell them whether or not the reactions they've been experiencing are signs of a histamine intolerance.
Unfortunately, that isn't the case: a normal blood test does not rule out - or in - histamine intolerance.
The truth is that diagnosing histamine intolerance is complex. It isn't as simple as measuring a single substance in your blood at one point in time. Your body's histamine levels are constantly in flux. In this article we'll explore why a blood test is an unreliable indicator of histamine intolerance, and what the more clinically accepted diagnostic path looks like.
Understanding Your Histamine Bucket
To understand why blood tests fall short, we need to think about the 'Histamine Bucket'. Imagine everyone has a bucket of a certain size, representing their personal threshold for histamine. As long as the total amount of histamine in your body stays below the brim of the bucket, you feel fine. When the bucket overflows, you experience reactions.
This bucket is filled from two main sources:
- External (Exogenous) Histamine: This is the histamine you consume through food and drink. Aged cheeses, cured meats, fermented foods, wine, and even some fruits and vegetables are high in histamine
- Internal (Endogenous) Histamine: This is the histamine your own body produces. It's released by immune cells (like mast cells) in response to allergens, stress, hormonal fluctuations, and even some medications
A blood test only measures the total amount of histamine circulating in your bloodstream at the precise moment of the test. It’s a single snapshot of a constantly changing picture. It can't tell you the size of your bucket, how quickly you fill it, or how efficiently you empty it.
The Problem with a Histamine Blood Test
Your histamine levels can swing dramatically throughout a single day. A reading that says that you aren't reactive to histamine might just mean your bucket wasn't overflowing at that exact moment. Here are just a few factors that can influence the result:
- Your Last Meal: Did you have a low-histamine breakfast of porridge and berries, or did you finish leftover curry from the night before? What you eat has a direct and immediate impact
- Stress Levels: A stressful commute or a difficult meeting can trigger your body to release its own internal histamine, temporarily raising your levels
- Your Hormonal Cycle: Oestrogen can stimulate mast cells to release histamine and can also down-regulate the DAO enzyme that clears it. Levels can be very different depending on where you are in your cycle
- Medications: Many common medications can either block the DAO enzyme or trigger histamine release, affecting your levels. Antihistamines work to stop your mast cells from producing histamine, which would negatively impact the results of a test
Because of this constant fluctuation, a single test is not a reliable indicator of an underlying intolerance. It’s like trying to judge the entire day's weather by looking out the window for just one second.
What About a DAO Blood Test?
Some healthcare providers may suggest a blood test to measure the activity of Diamine Oxidase (DAO). DAO is the primary enzyme responsible for breaking down the histamine you consume from food and drink. It’s estimated that up to 80% of histamine intolerance cases are related to DAO deficiency.
Initially this might sound more promising, but a DAO blood test has its own limitations. A blood test provides an indirect measurement that may not accurately reflect the enzyme’s activity in your gut, where it’s most needed to process the food you eat. DAO however does most of its important work in the lining of your small intestine, helping to prevent the histamine that you ingest in your diet from entering your bloodstream.
While some studies suggest a correlation between low DAO in the bloodstream and histamine intolerance, it should not be considered a definitive diagnostic tool on its own. It might serve as another clue, it will only ever be another piece of the puzzle.
So How Is Histamine Intolerance Actually Diagnosed?
Given the unreliability of testing, the most recognised and trusted method for diagnosing histamine intolerance is a supervised elimination diet.
This is typically a two-stage process, which should always be undertaken with the guidance of a registered dietitian or a qualified healthcare professional to ensure it is done safely and that your nutritional needs are met.
- The Elimination Phase: For a short period, usually two to four weeks, you follow a strict low-histamine diet. The goal is to lower the overall level in your 'histamine bucket' and see if your symptoms improve. This provides a baseline
- The Reintroduction Phase: If you feel better, you then begin to systematically reintroduce higher-histamine foods one at a time, in a controlled way. This careful process helps you identify which specific foods are problematic for you and, just as importantly, what your personal tolerance threshold is
This approach is the diagnostic gold standard because it’s tailored to you. It respects that everyone’s 'bucket' and triggers are unique. If you're looking for an expert to guide you, we list a number of independent dietitians who specialise in histamine intolerance on our About page.
Trust Your Body and Seek the Right Support
By understanding the limitations of blood tests, we hope that you can have more informed conversations with healthcare professionals and find a way forward that works for you. If you’ve already had a blood test and been told your tests are normal, but you know something isn’t right, know that you aren't alone.