Test Guide
Always Tired? What Your Biomarkers Might Reveal
Constant tiredness is one of the most common reasons people consider a blood test. Several biomarkers are often involved: iron stores, thyroid function, vitamin B12 and folate, vitamin D, blood count and inflammation. Biomarker testing can highlight underlying factors that may contribute to how you feel. It is not a diagnostic tool. The information below is educational and does not replace personalised medical advice.
Biomarker patterns commonly linked with fatigue
Low ferritin (iron stores): Iron deficiency typically shows in ferritin before red cell counts drop, so fatigue can be present without anaemia on a basic blood count.
Underactive thyroid: Elevated TSH with low or low-normal free T4 and free T3 is a classic pattern. What people often describe includes fatigue, cold intolerance and weight changes.
Vitamin B12 or folate deficiency: Causes a specific type of anaemia and can also cause neurological effects including fatigue and brain fog.
Low vitamin D: Common in the UK in winter months. Linked with fatigue, low mood and reduced exercise tolerance.
Raised CRP (inflammation): Suggests an ongoing inflammatory process worth investigating with a clinician.
When fatigue is not just biomarkers
Many causes of fatigue do not show on blood tests. Sleep quality, sleep disorders such as sleep apnoea, mental health, chronic pain, medication side effects and long-term stress are all major drivers and need separate assessment.
Treating biomarker results as one input alongside a wider picture is far more useful than relying on numbers alone.
What about chronic fatigue syndrome (ME/CFS)?
ME/CFS is a clinical diagnosis made by a doctor. Blood tests are typically used to rule out other causes before that diagnosis is considered, rather than to confirm it. Anyone with months of unexplained, severe fatigue should be assessed by their GP.
Related: Best Blood Test for Fatigue
Our full guide to fatigue testing, panels compared and what to expect.
Chxhealth panels that cover these markers
The panels below cover the biomarkers discussed above. Each comes with a plain English PDF report, lab analysis by Randox (UKAS, ISO 15189), and the phlebotomy fee included in the price.
Tired All The Time
Our most comprehensive fatigue-focused panel covering iron, thyroid, B12, folate, vitamin D, full blood count and inflammation.
Anaemia Profile
A deeper look at iron, B12 and folate when anaemia is suspected.
Thyroid Health
Focused thyroid panel for cold intolerance, weight changes and mood changes alongside fatigue.
Iron Status
Targeted iron panel when iron is the most likely cause.
Related biomarker guides
Read more about the markers discussed in this guide:
FAQs
Could a blood test tell me why I am tired?
It can flag common biomarker patterns linked with fatigue, such as low iron, low thyroid or low B12. It does not diagnose fatigue and many causes do not show in blood. Discuss results with your clinician.
What is the most useful single test for fatigue?
Ferritin (iron stores) is often the highest-yield single marker, especially in women of reproductive age. A broader panel is usually more informative.
When should I see my GP about tiredness?
Sooner rather than later if your tiredness is severe, has come on quickly, is worsening, or comes with weight loss, night sweats, fevers or new pain. Use NHS 111 if you are unsure.
Do I need to fast for a fatigue panel?
Most fatigue-focused panels do not strictly require fasting, but check the product page. Fasting is sometimes recommended if metabolic markers are included.
About this guide. These tests provide biomarker data only. They do not diagnose any condition. Always discuss your results with a qualified clinician before making decisions about your health, medication or lifestyle. Educational content for general awareness. Chxhealth provides biomarker and genetic data. We do not diagnose, treat or prescribe. For medical advice about your health or results, please speak to a qualified clinician.