Chronic Fatigue Syndrome (CFS) & Functional Testing: What Actually Needs Looking At

One of the biggest reasons people remain stuck with chronic fatigue is that the right things are never investigated.

GPs, and even most private doctors, simply do not run these assessments. Not because they are unimportant, but because they fall outside the conventional medical model. These are functional tests, and they are ordered, interpreted, and applied through a trained practitioner.

This distinction matters. Results without context are not only unhelpful, they can actively mislead.

When I work with someone experiencing chronic fatigue, testing is always guided by their full clinical picture. There is no standard panel and no one-size-fits-all approach. However, there are key systems that should never be ignored.

Gut and Digestive Function

The gut plays a central role in energy production, immune regulation, inflammation control, and nutrient absorption. Functional assessment looks at digestion, microbial balance, immune activity, and gut integrity. Ongoing gut dysfunction is extremely common in chronic fatigue and is rarely addressed in standard care.

Mitochondrial and Energy Pathways

Fatigue is not imagined. In many cases, energy is simply not being produced efficiently at a cellular level. Functional testing allows us to understand whether the body has the raw materials and biochemical capacity to generate energy, rather than assuming the issue is psychological.

Stress Response and Cortisol Rhythm

Many people with chronic fatigue are not simply stressed. Their nervous system has adapted into patterns that continually drain energy. Functional testing looks at how cortisol is being produced and regulated across the day, which often explains why people feel wired and tired at the same time.

Hormonal Signalling Beyond Basic Blood Tests

Standard blood tests look for disease. Functional testing looks at how hormones are being produced, converted, and utilised. Subtle imbalances can have a profound impact on energy, sleep, mood, and resilience without ever triggering a medical diagnosis.

Inflammation and Immune Activation

Low-grade, chronic inflammation is one of the most overlooked drivers of fatigue. Functional testing can identify ongoing immune activation and inflammatory stressors that are not visible on routine testing.

Nutrient Status at a Functional Level

Blood tests often show results within reference ranges while cells are functionally depleted. Magnesium, B vitamins, amino acids, fatty acids, and trace minerals are all essential for energy production. Functional testing helps determine whether nutrients are actually being absorbed and used.

Toxic Burden and Detoxification Capacity

Environmental toxins, chemicals, mould exposure, and metabolic waste place a significant load on the body. If detoxification and clearance pathways are under strain, fatigue, brain fog, and inflammation often follow. Functional testing can assess toxic burden and the body’s ability to process and eliminate it effectively.

Why These Tests Are Not for Self-Ordering

These tests are not designed to be interpreted in isolation.

Without understanding symptom patterns, timelines, interactions between systems, and the correct order in which imbalances should be addressed, people often end up overwhelmed or chasing the wrong issue.

This is why functional testing is ordered by a practitioner, interpreted in context, and used to guide a structured, personalised plan. It is not a shopping list of supplements or another layer of confusion.

The Bigger Picture

Chronic fatigue is rarely caused by one problem. It is what happens when multiple systems are under sustained strain.

Functional testing allows us to stop guessing and start understanding, but only when it is done properly and with someone who knows how to connect the dots.

If you are living with ongoing fatigue and being told everything looks fine, that does not mean nothing is wrong. It often means the right questions have not been asked yet.

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