Clinical Correlation · Philosophy of Practice · Test, Don't Guess
There is a moment in clinical practice — not every session, but often enough to recognise it — when the test results stop being numbers and become a portrait. The HPA axis data maps the chronic stress picture the client described in the intake form. The OAT gut dysbiosis markers explain why the brain fog started after the course of antibiotics three years ago. The low vitamin C explains why the tissue hasn't healed. The elevated HVA/VMA ratio explains why motivation has been so elusive. The data and the person align. Reed Davis calls this clinical correlation. After nearly forty years’ experience working with people, I call it the Mirror Moment — the point at which the client sees themselves in their own data, often for the first time. It changes everything about how they engage with what comes next.
Reed Davis, who developed the Functional Diagnostic Nutrition framework and whose training shaped my clinical approach, uses clinical correlation to describe something precise: the alignment between what a client reports in their history, what their symptoms indicate, and what the functional laboratory data shows. When these three sources of information converge on the same picture — when they tell the same story in different languages — that is clinical correlation.
It sounds simple. In practice, it is the hardest and most important skill in functional medicine. It requires enough clinical history to understand the person's story in full. It requires test results that measure the right systems at the right resolution. And it requires the pattern recognition to see the connection between a cortisol curve collected on dried urine strips and a client who hasn't felt rested after sleep in four years.
What it is not — and this is equally important — is treating the test result. Reed makes this distinction explicitly and it is one of the most valuable things he teaches. The test result tells you where to look. It does not tell you what to do. Two people can have identical HPHPA elevations on their OAT and require completely different interventions depending on the clinical history, the other markers, and the full picture of what their life looks like. The data informs the person. It does not replace them.
The test result is not the patient. The pattern across multiple tests, read through the lens of a complete clinical history, in the context of a person's actual life — that is where the clinical picture lives. The data is the map. The person is the territory.
Let me give you an example that reflects the kind of clinical picture I see regularly — a constructed composite, not any individual client.
A woman in her late forties. Bloating that starts within an hour of eating and builds through the day, worse after onions, garlic and beans. Bowels sluggish for years. Omeprazole for reflux, started "for a few weeks" and still being repeated six years later. A course of antibiotics for a chest infection shortly before the bloating became constant. Tired by mid-afternoon, and she has stopped mentioning the brain fog because nobody asked about it.
When the results come back, they tell me this:
When I go through this with a client — not reading them a lab report, but translating the pattern into plain language and connecting it to what they told me in their history — there is a moment when they go quiet. Then they say something like: "That's exactly right. That's exactly what's been going on." That is the Mirror Moment. Not the data. The recognition.
People who have been unwell for years — who have been told their tests are normal, who have been offered antidepressants for fatigue, who have been told to eat less and exercise more without anyone asking what their cortisol looks like at 2pm — often arrive at a functional medicine consultation with a specific mixture of hope and exhaustion. They want an explanation. They have had symptoms explained away for so long that the experience of having something explained accurately is genuinely unusual.
When the data reflects their experience back to them accurately, it does several things simultaneously. It validates what they have known intuitively — that something is measurably wrong, not just subjectively felt. It removes the self-blame that accumulates when the system repeatedly tells you there is nothing to find. It creates a rational basis for the protocol that follows — not "trust me and take these supplements" but "here is the data, here is the mechanism, here is the sequenced intervention that addresses what the data shows." And it establishes the clinical relationship on a foundation of shared understanding rather than asymmetric authority.
The Mirror Moment is not a therapeutic technique. It is the natural consequence of doing the assessment correctly — gathering enough history, running the right tests, and reading the results with the person rather than at them. But its effect on clinical engagement is profound. A person who understands their own data is more likely to follow the protocol, more likely to notice what is changing, and more likely to return when something shifts. They have been given a framework for understanding their own body that extends beyond this particular consultation.
The highest value I can offer a client is not a protocol. It is a map of what is happening in their specific biochemistry — and the explanation of why it is happening in a way that connects to the life they have described. Anyone can read a lab report. The clinical skill is in seeing the person in the data.
This principle — treating the person, not the test result — sounds obvious when stated. It is violated constantly in clinical practice, both conventional and functional. In conventional medicine, the violation looks like prescribing to a number: a TSH above threshold triggers levothyroxine regardless of the person's symptom picture, age, lifestyle, or other clinical context. In functional medicine, the violation looks like supplement stacking to individual markers: HPHPA elevated, therefore Clostridium protocol; 5-HIAA low, therefore 5-HTP; ferritin low, therefore iron. Each decision reasonable in isolation. None of them constituting clinical practice in the meaningful sense.
Clinical practice — real clinical practice — requires holding the data and the person simultaneously. Knowing that the HPHPA is elevated and also knowing that this particular person with this particular history in this particular life context requires a specific kind of intervention at a specific pace. Knowing that the 5-HIAA is low and also knowing that this person's serotonin depletion is being driven by IDO pathway diversion from systemic inflammation — so that 5-HTP without addressing the inflammation will achieve limited results and the inflammation needs to be the first priority.
Sources for the case box: breath-test thresholds, Rezaie et al., Am J Gastroenterol 2017, PMID 28323273, doi:10.1038/ajg.2017.46; methane and constipation, Kunkel et al., Dig Dis Sci 2011, PMID 21286935, doi:10.1007/s10620-011-1590-5.
This is what nearly forty years of pattern recognition looks like. Not accumulated knowledge stored in a filing cabinet but embodied understanding — the ability to see a test result and know immediately what questions it raises about the person, what other data it needs to be read alongside, and what it means in the context of the story that brought this particular person to this particular consultation.
The TDG philosophy — Test, Don't Guess — is sometimes misread as a commitment to data over everything else. Run enough tests and the protocol writes itself. This misses what the phrase actually means clinically.
Testing without guessing is not the same as testing without thinking. The test tells you what is present. The clinical skill tells you what it means — which requires a complete history, a willingness to sit with the complexity of a real person's real life, and the pattern recognition to see the picture that emerges when all three sources of information converge.
The five-test TDG programme measures five different sample types. Those data points are not the clinical picture — they are the raw material of it. The clinical picture emerges when the data is read alongside the history, translated into the language of the person's lived experience, and integrated into an understanding of the person that encompasses their biology, their behaviour, their environment, and their story.
That integration — when it happens, when the picture coheres, when the client goes quiet and then says "yes, that's exactly it" — that is the Mirror Moment. It is not the most technically impressive thing about this approach. It is the most important thing about it. Because the protocol that follows from that moment lands in a completely different way than a protocol delivered without it. The person is not receiving recommendations. They are receiving an explanation of themselves. And that changes everything about what they do with what comes next.
The TDG Five-Test Programme — five simultaneous functional panels, a complete clinical history, and an interpretation that connects the data to your specific story. The Mirror Moment is the aim. The test results are the means.
Book a free 20-minute call →