Common Medical Causes
| Cause | Clue Symptom | Key Test |
|---|---|---|
| Iron deficiency anaemia | Pale skin, cold hands, brittle nails | Ferritin, FBC |
| Hypothyroidism | Weight gain, cold intolerance, constipation | TSH, Free T4 |
| Type 2 diabetes | Thirst, frequent urination | Fasting glucose, HbA1c |
| Sleep apnoea | Snoring, morning headache | Sleep study (polysomnography) |
| Depression / anxiety | Low mood, anhedonia | Clinical assessment |
| Coeliac disease | Bloating, diarrhoea | tTG-IgA antibody |
| Chronic kidney disease | Swelling, foamy urine | eGFR, urea, creatinine |
| ME/CFS | Post-exertional worsening | Diagnosis of exclusion |
Start With Blood TestsAsk your GP for: FBC, ferritin, TSH, fasting glucose, U&E, LFTs, CRP, and vitamin D. These cover the most common and easily-treated causes.
When Is Fatigue 'Normal'?
Short-term fatigue after illness, intense exercise, or major life stress is expected. Fatigue lasting more than 4–6 weeks with no clear cause warrants investigation.
What blood tests should I have for tiredness?
The core panel: FBC (anaemia), ferritin (iron stores), TSH (thyroid), fasting glucose or HbA1c (diabetes), vitamin D, CRP (inflammation), and kidney/liver function.
Can vitamin D deficiency cause extreme fatigue?
Yes. Severe vitamin D deficiency is associated with muscle aches, low mood, and fatigue. A simple blood test confirms it; supplementation usually helps.
Is fatigue a sign of cancer?
Unexplained persistent fatigue — especially with weight loss, night sweats, or lumps — warrants urgent GP assessment. Most fatigue is not cancer, but red-flag symptoms should be evaluated.
How is ME/CFS diagnosed?
ME/CFS is diagnosed after other causes are excluded. The hallmark is post-exertional malaise — fatigue that worsens significantly after physical or mental activity.
Medical Disclaimer: This page is for general education only and does not replace professional medical advice. Always consult a qualified healthcare provider.