Functional Diagnostic Nutrition
in the United Kingdom

The DUTCH Plus is widely regarded as the most advanced dried urine hormone test available. It covers the full HPA axis including diurnal cortisol and cortisone patterns, DHEA-S, all major sex hormones and their metabolites, oestrogen detoxification pathways (2-OH, 4-OH, 16-OH), and melatonin. It does not include secretory IgA, which the FDN saliva panel does. Available through Regenerus Labs with UK postal collection kits — no clinic visit required. Urine rather than saliva, so it is a close equivalent rather than an identical test, and in several respects more comprehensive.

The FDN Metabolic Wellness Profile is a targeted organic acids panel covering protein digestion (Indican), liver detoxification (Urinary Bile Acids), and oxidative stress (8-OHdG). A full organic acids test goes much further — mitochondrial function, neurotransmitter metabolites, B-vitamin markers, and yeast and bacterial markers — but panels differ, and not every OAT includes urinary bile acids or 8-OHdG. Check the specific panel before treating it as a like-for-like swap. UK postal collection kit.

The FDN Mucosal Barrier Assessment measures zonulin, histamine and DAO. The Precision Point Diagnostics Advanced Intestinal Barrier Assessment, available through Regenerus Labs, measures zonulin, DAO and LPS (lipopolysaccharide, a bacterial endotoxin), as a home blood collection kit. One caution applies to serum zonulin wherever it’s measured. A 2019 Monash study found that two widely used commercial serum zonulin assays were not detecting zonulin at all, but other proteins such as complement C3 and haptoglobin, and advised caution in using serum zonulin as a barrier marker (Ajamian et al., PLoS One 2019). So I don’t recommend it as a substitute, and I don’t offer zonulin testing. For the gut barrier I look at the GI-MAP immune markers (sIgA, calprotectin) and the clinical picture.

The GI-MAP is the same test in the UK as in the US — Diagnostic Solutions Laboratory produces it, and Regenerus Labs distribute it to UK practitioners with postal stool collection kits. No substitution is required. The GI-MAP uses quantitative PCR DNA analysis to identify pathogens, parasites, H. pylori, opportunistic bacteria, beneficial microbes, and intestinal immune markers including sIgA, calprotectin, and lactoferrin. This is the most straightforward of the five tests for UK implementation — clinically identical in every respect.

The FDN programme uses the Mediator Release Test (MRT) — a US-only test measuring functional immune reactivity across 176 foods and chemicals via mediator release rather than antibody measurement. MRT is not available to UK clients. The TDG framework uses the HealthBeings IgG food panel (286 foods) — a home collection kit available to UK clients covering 286 foods, including spices, yeasts and novel ingredients. The mechanism differs from MRT: IgG measures antibody-mediated memory responses rather than immediate mediator release. The evidence for both is weak. Food-specific IgG largely reflects which foods a person has been eating, and the European allergy academy (EAACI) advises against IgG4 food testing for diagnosing food intolerance (Stapel et al., Allergy 2008). MRT has little independent published validation either. Where I use a food panel, it is a prompt for a supervised elimination and reintroduction, not a list of foods to cut.

The FDN programme incorporates Metabolic Typing® as developed by Bill Wolcott — a questionnaire-based assessment determining optimal macronutrient ratios by metabolic type. The TDG framework uses its own model instead, Metabolic Natures: two axes and six positions, starting from a questionnaire and checked against test findings and how a person actually responds. It is a starting point to be tested on the individual, not a diagnosis, and it has not been validated in a trial.

Comprehensive blood chemistry is not part of the standard FDN five-test suite. The TDG framework adds Regenerus blood chemistry as a fifth integrated layer — covering, depending on the panel, a full metabolic panel, thyroid (TSH, free T4, free T3, reverse T3, TPO antibodies), iron studies (ferritin, serum iron, TIBC, transferrin saturation), cardiovascular markers, inflammatory markers (CRP, homocysteine), liver function, and kidney function. Markers are read against the laboratory range and, where there is a stated source for one, a tighter clinical threshold. Ferritin is the clearest example: 18 µg/L sits inside many laboratory reference ranges, yet NICE guidance treats a ferritin below 30 µg/L as confirming iron deficiency (NICE CKS). This is the layer that makes TDG an advanced implementation of FDN methodology rather than a direct replica.