Fatigue is the most common symptom our customers report. It is also the most common symptom GPs struggle to explain with a basic blood test. The reason is simple: fatigue can come from at least eight different health systems, and a standard GP panel checks two or three of them.
When you tell your GP you are tired, they might check your haemoglobin and thyroid (TSH). If those are normal, you are told nothing is wrong. But fatigue has at least eight biochemical drivers, and a standard GP test checks one or two of them. Here is what a comprehensive blood test actually looks for.
This is the most common nutritional cause of fatigue globally. Your GP checks haemoglobin, which only drops when iron deficiency is severe enough to cause anaemia. Long before that happens, low ferritin depletes your body's iron stores, reducing oxygen transport efficiency, mitochondrial function, and energy production. A ferritin of 15 is "within range" at most labs but is far from optimal. Full iron studies (ferritin, serum iron, TIBC, transferrin saturation) catch depletion at the earliest stage.
Your GP checks TSH. If it is within range, your thyroid is declared normal. But TSH alone misses conversion problems where your body produces enough T4 but does not convert it efficiently to T3, the active hormone that drives metabolic rate. A normal TSH with low Free T3 leaves you fatigued, cold, mentally foggy, and gaining weight. Thyroid antibodies catch autoimmune thyroid disease (Hashimoto's) before TSH even moves. TrueVitals tests TSH, Free T3, Free T4, and antibodies in every panel.
Endemic in the UK, especially between October and April. A vitamin D level of 30 nmol/L is technically within range at some labs but is associated with fatigue, low mood, poor immune function, and muscle weakness. Optimal is 75 to 125 nmol/L. If your GP tests it at all, they often only flag levels below 25. A comprehensive test shows you where you sit relative to optimal, not just whether you are clinically deficient.
Low testosterone causes fatigue in both men and women. But total testosterone alone is misleading without SHBG (which determines how much is actually available) and cortisol (which suppresses testosterone when chronically elevated). In women, low progesterone disrupts sleep quality, and elevated prolactin causes persistent tiredness. A complete hormonal panel shows the full endocrine picture rather than one number in isolation.
When your cells become resistant to insulin, glucose regulation becomes inefficient. Your blood sugar swings between highs and lows, producing energy crashes, brain fog, and persistent tiredness, even when HbA1c and fasting glucose still look normal. Fasting insulin and HOMA-IR catch insulin resistance at the earliest stage, years before glucose markers shift. Most GPs do not test insulin unless diabetes is already suspected.
Both are essential for red blood cell production, neurological function, and energy metabolism. Deficiency causes fatigue, brain fog, poor concentration, and mood changes. Common in vegetarians, vegans, people on metformin or PPIs, and women on the contraceptive pill. Your GP might check B12 but rarely checks folate or red cell folate (which gives a longer-term picture than serum folate).
Persistent low-level inflammation drives fatigue, joint stiffness, brain fog, and poor recovery. hs-CRP (high-sensitivity C-reactive protein) quantifies systemic inflammation. A "normal" CRP does not mean inflammation is absent. Optimal hs-CRP is below 1.0 mg/L. A result of 2.5 is within the reference range but associated with increased cardiovascular risk and chronic fatigue. TrueVitals reports flag suboptimal results, not just clinically abnormal ones.
Chronic stress keeps cortisol elevated, which suppresses testosterone, disrupts sleep architecture, impairs glucose regulation, and produces a wired-but-tired state. Eventually the HPA axis becomes blunted and cortisol drops too low, producing profound fatigue, poor stress tolerance, and inability to recover. A morning cortisol level in context with DHEA-S and testosterone gives you a clear picture of your stress axis.
Your GP is not wrong. Based on the markers they tested, your results were within the reference range. The problem is what they did not test.
A typical GP fatigue investigation checks haemoglobin, basic liver and kidney function, TSH, and sometimes fasting glucose. That is approximately 10 markers across 3 health systems. If those are normal, there is nothing left to investigate with the tools available.
A TrueVitals Ultimate panel checks 114 markers across every major health system simultaneously, including every cause of fatigue listed above. It also highlights suboptimal results, not just clinically abnormal ones. A vitamin D of 32 is "normal" on a GP printout. On a TrueVitals report, it is flagged as suboptimal with a specific supplementation recommendation.
This is not about replacing your GP. It is about giving both you and your GP deeper data to work with. See our full NHS vs private comparison.
Fatigue is rarely caused by a single marker in isolation. It is usually a combination. Low iron plus suboptimal thyroid plus poor vitamin D plus elevated cortisol produces a fatigue that no single treatment will fix. You need to see all the contributing factors simultaneously to understand which interventions will actually help.
This is exactly what TrueVitals' AI-powered reporting does. It processes over 6,400 pairwise interactions across the Ultimate panel, cross-references them with your lifestyle quiz data (sleep quality, stress levels, exercise habits, dietary patterns, symptoms), and identifies the combination of factors driving your fatigue. The report then gives you specific, prioritised recommendations.
Testing one system at a time with separate appointments over weeks or months wastes time and misses the connections. One comprehensive test shows you the full picture in 48 hours. See how our reports work.
Your report identifies the specific markers driving your fatigue and gives you targeted recommendations. Iron supplementation with specific forms and timing. Vitamin D dosing based on your current level. Thyroid follow-up guidance. Share your report with your GP if clinical intervention is needed.
This is the most common scenario. Your report prioritises the interventions most likely to have the biggest impact. Address the worst deficit first, retest in 3 to 6 months to confirm improvement, then move to the next factor.
Ruling out biochemical causes of fatigue is genuinely useful. It narrows the investigation to sleep quality, stress management, training load, or other non-blood factors. Your report still provides a comprehensive health baseline for future comparison.
Your report flags anything that warrants GP involvement and explains what to discuss. Share the PDF directly with your doctor. A 114-marker report gives your GP significantly more data than a standard NHS blood test printout.
A comprehensive panel that covers full iron studies, complete thyroid (TSH, FT3, FT4, antibodies), hormones (testosterone, cortisol, DHEA-S), metabolic markers (HbA1c, insulin), vitamin D, B12, folate, magnesium, and hs-CRP. TrueVitals Ultimate (114 markers, £349) covers all of these and more. View the Ultimate panel.
A GP fatigue workup typically checks approximately 10 markers (haemoglobin, liver, kidney, TSH, glucose). These can all be within range while you are iron-depleted (ferritin is more sensitive than haemoglobin), thyroid-suboptimal (Free T3 is more informative than TSH), or vitamin D deficient at a level technically "in range" but far from optimal. A comprehensive test checks all eight systems that cause fatigue simultaneously.
There is no single blood test for ME/CFS. However, a comprehensive panel is an essential diagnostic step because it identifies or rules out treatable causes of fatigue: thyroid dysfunction, iron deficiency, vitamin deficiencies, hormonal imbalances, insulin resistance, and chronic inflammation. Ruling these out is part of the ME/CFS diagnostic pathway.
TrueVitals delivers your full report within 48 hours of your blood draw. Your report includes personalised analysis of every marker relevant to fatigue, cross-system pattern identification, and specific recommendations.
The Ultimate panel (114 biomarkers, £349) is the best choice for investigating fatigue because it covers all eight systems that cause tiredness. The Advanced panel (74, £269) covers most but misses insulin resistance profiling and tumour markers. If you want the deepest possible investigation, the Signature panel (200+, £799) adds neurological markers and autoimmune profiling. Take the quiz for a personalised recommendation.
114 biomarkers across every system that causes fatigue. AI-powered cross-system analysis. Answers in 48 hours.
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